V4 Use EXIF byte order for EXIF encoded strings.

[JimBobSquarePants]

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Description

Fixes #2906

When decoding Unicode-encoded text from EXIF, we should follow the specification's guidance and determine the correct decoding approach based on the following priority:

1. Check for a Byte Order Mark (BOM):
   If a BOM is present at the start of the encoded string, its endianness should override any other assumptions. This is explicitly allowed by the EXIF 2.2 and 2.3 specifications, even though later versions (e.g., CIPA DC-X008-2019) no longer mention it directly.

2. Fallback to TIFF Byte Order:
   If no BOM is present, the byte order of the Unicode text must match the byte order declared in the TIFF header. This was the originally intended behavior according to EXIF 2.2/2.3, and is still necessary for correctly decoding existing conformant files.

This change ensures that we're correctly interpreting the UserComment, GPSProcessingMethod, and GPSAreaInformation tags, all of which use the 8-byte encoding prefix scheme and may contain UTF-16 encoded text.

On encoding, we now honor the TIFF byte order for Unicode strings and optionally support emitting a BOM when desired.

This brings ImageSharp into alignment with the EXIF specification and improves compatibility with real-world image metadata.

In addition to this fix, I've also correctly reimplemented the equality operators for ExifTag and performed code quality cleanup to match standards.

[Copilot]

Pull Request Overview

This PR updates EXIF metadata handling to correctly use the TIFF byte order for decoding and encoding EXIF encoded strings while cleaning up and modernizing the code.

• Implements BOM detection and byte order handling for Unicode encoded strings.
• Applies new C# pattern matching and array initializer syntax throughout the EXIF value implementations.
• Improves XML documentation and equality operator implementations for ExifTag.

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
IExifValue.cs	Updated XML comments and added explicit public member modifiers.
ExifSignedShortArray.cs, ExifSignedShort.cs, ExifSignedByte.cs, ExifShortArray.cs, ExifShort.cs, ExifRationalArray.cs, ExifNumberArray.cs	Refactored value range checks and array initializations to use new C# syntax patterns.
ExifEncodedString.cs	Changed TrySetValue to accept a ByteOrder parameter with a parameterless wrapper defaulting to LittleEndian.
ExifByteArray.cs, ExifByte.cs, ExifArrayValue{TValueType}.cs	Updated array initializer syntax for brevity.
ExifTag.cs	Revised operator overloads and documentation capitalization.
ExifWriter.cs, ExifReader.cs, ExifProfile.cs, ExifEncodedStringHelpers.cs, ExifDataType.cs, Ifd/EntryReader.cs	Modernized collection initializations and applied minor name/style updates.