Not support Unicode Khmer with "Coeng" sign (្)

[DyDev-1]

Describe the bug

When generating a PDF invoice using the pdf package, the Khmer script's "Khmer Sign Coeng" (្) is not rendering correctly with Khmer letters. This diacritical mark, essential for forming certain consonant clusters, fails to combine properly with the preceding and following Khmer characters, resulting in incorrect and unreadable text.
Example
Correct Rendering: បន្ទាត់ (a valid Khmer word)
Incorrect Rendering:

(shows the issue with "Khmer Sign Coeng" not combining correctly)

To Reproduce
Code snippet to reproduce the behavior:

  Future<String> generatePdfInvoice(PdfPageFormat format, List<Invoice> invoiceItems) async {
    final pdf = pw.Document();
    final img = await rootBundle.load('assets/images/header_invoice.png');
    final imageBytes = img.buffer.asUint8List();
    // final khmerFont = pw.Font.ttf(await rootBundle.load('assets/fonts/Khmer-OS-Siemreap-Regular.ttf'));
    final Uint8List fontData = base64Decode(khmerFontBase64);
    final khmerFont = pw.Font.ttf(fontData.buffer.asByteData());


    // Define the maximum number of items per page
    const int itemsPerPage = 33;

    // Split the invoice items into chunks of itemsPerPage
    List<List<Invoice>> chunks = [];
    for (var i = 0; i < invoiceItems.length; i += itemsPerPage) {
      chunks.add(invoiceItems.sublist(
        i,
        i + itemsPerPage > invoiceItems.length ? invoiceItems.length : i + itemsPerPage,
      ));
    }

    // Add a page for each chunk of invoice items
    for (var i = 0; i < chunks.length; i++) {
      final chunk = chunks[i];
      pdf.addPage(

        pw.MultiPage(
          theme: pw.ThemeData.withFont(
            base: khmerFont,
          ),
          pageFormat: PdfPageFormat.a4,
          build: (pw.Context context) {
            return <pw.Widget>[
              if (i == 0)
                pw.Container(
                  alignment: pw.Alignment.center,
                  child: pw.Image(pw.MemoryImage(imageBytes)),
                ),
              if (i == 0)
                pw.Container(
                  child: pw.Divider(
                    height: 1,
                    thickness: 1,
                    indent: 1,
                    endIndent: 0,
                    color: PdfColor.fromHex("#000000"),
                  ),
                ),
              pw.SizedBox(height: 20),
              if (i == 0)
                pw.Row(
                  children: [
                    pw.Container(
                      child: pw.Row(
                        children: [
                          pw.Column(
                              crossAxisAlignment: pw.CrossAxisAlignment.start,
                              children: [
                                pw.Text("Billed To", style: pw.TextStyle(color: PdfColor.fromHex("#5453C6"))),
                                pw.Text("Client Name : ${nameController.text.toString()}"),
                                pw.Text("Address : ${addressController.text.toString()}"),
                                pw.Text("Tel: ${telController.text.toString()}"),
                              ]
                          ),
                          pw.SizedBox(width: 80), // Add horizontal space between text elements
                          pw.Column(
                              mainAxisAlignment: pw.MainAxisAlignment.center,
                              children: [
                                pw.Text("Date Issued", style: pw.TextStyle(color: PdfColor.fromHex("#5453C6"))),
                                pw.Text("${dateController.text.toString()}"),
                              ]
                          ),
                          pw.SizedBox(width: 15),
                          pw.Column(
                              mainAxisAlignment: pw.MainAxisAlignment.center,
                              children: [
                                pw.Text("Invoice Number", style: pw.TextStyle(color: PdfColor.fromHex("#5453C6"))),
                                pw.Text("${numController.text.toString()}"),
                              ]
                          ),
                        ],
                      ),
                    ),
                  ],
                ),
              pw.SizedBox(height: 20),

              // Table construction using pw.Table.fromTextArray
              pw.Table.fromTextArray(
                border: null,
                cellAlignment: pw.Alignment.center,
                headerDecoration: pw.BoxDecoration(color: PdfColors.grey300),
                headerHeight: 30,
                cellHeight: 30,
                headerStyle: pw.TextStyle(fontWeight: pw.FontWeight.bold, font: khmerFont),

                headers: ['No', 'Description', 'Qty', 'Unit Price', 'Amount'],
                data: List<List<dynamic>>.generate(
                  chunk.length,
                      (index) => [
                    '${index + 1}',
                    chunk[index].description,
                    chunk[index].qty,
                    pw.Text(
                      '${chunk[index].price} ${chunk[index].cur == "R" ? "\R" : "\$"}',
                      style: pw.TextStyle(fontSize: 12),
                    ),
                    '${chunk[index].qty * chunk[index].price} ${chunk[index].cur == "R" ? "\R" : "\$"}',
                  ],
                ),
              ),

              pw.SizedBox(height: 20),
              if (i == chunks.length - 1)
                pw.Row(
                    mainAxisAlignment: pw.MainAxisAlignment.end,
                    children: [
                      pw.Column(
                        mainAxisAlignment: pw.MainAxisAlignment.end,
                        children: [
                          pw.Text('Total Amount Riel: ${totalRController.text} R',
                              style: pw.TextStyle(fontWeight: pw.FontWeight.bold)),
                          pw.Text('Total Amount USD : ${totalUController.text} \$',
                              style: pw.TextStyle(fontWeight: pw.FontWeight.bold)),
                          pw.Text('Total Due Amount Riel : ${totalDueRController.text} R',
                              style: pw.TextStyle(fontWeight: pw.FontWeight.bold)),
                          pw.Text('Total Due Amount USD : ${totalDueUController.text} \$',
                              style: pw.TextStyle(fontWeight: pw.FontWeight.bold)),
                        ],
                      )
                    ]
                )

            ];
          },
        ),
      );
    }

    final output = await getTemporaryDirectory();
    final invoice_num =  numController.text;
    final file = File("${output.path}/${invoice_num.toString()}.pdf");
    await file.writeAsBytes(await pdf.save());
    return file.path;
  }

Expected behavior

The "Khmer Sign Coeng" (្) should combine seamlessly with preceding and following Khmer letters to form valid consonant clusters, ensuring that the text is rendered correctly and is readable.

Screenshots

Flutter Doctor

Desktop (please complete the following information):

• iOS
• Android
• Browser
• Windows
• Linux

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context