Add PopupMenuButton.iconColor, PopupMenuTheme.iconSize and fix button icon using unexpected color propert

[TahaTesser]

fixes PopupMenuButton uses color property for icon color
fixes popup_menu_test.dart lacks default icon color tests.

Description

• Add PopupMenuButton.iconColor and fix the PopupMenu button icon using an unexpected color property.
• Add the missing PopupMenuTheme.iconSize.
• Clean up some tests and minor improvements.

Code sample

expand to view the code sample

import 'package:flutter/material.dart';

/// Flutter code sample for [PopupMenuButton].

// This is the type used by the popup menu below.
enum SampleItem { itemOne, itemTwo, itemThree }

void main() => runApp(const PopupMenuApp());

class PopupMenuApp extends StatelessWidget {
  const PopupMenuApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        popupMenuTheme: PopupMenuThemeData(
          // iconSize: 75,
          // iconColor: Colors.amber,
          color: Colors.deepPurple[100],
        ),
      ),
      home: const PopupMenuExample(),
    );
  }
}

class PopupMenuExample extends StatefulWidget {
  const PopupMenuExample({super.key});

  @override
  State<PopupMenuExample> createState() => _PopupMenuExampleState();
}

class _PopupMenuExampleState extends State<PopupMenuExample> {
  SampleItem? selectedMenu;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('PopupMenuButton')),
      body: Center(
        child: PopupMenuButton<SampleItem>(
          iconSize: 75,
          // iconColor: Colors.amber,
          color: Colors.deepPurple[100],
          initialValue: selectedMenu,
          // Callback that sets the selected popup menu item.
          onSelected: (SampleItem item) {
            setState(() {
              selectedMenu = item;
            });
          },
          itemBuilder: (BuildContext context) => <PopupMenuEntry<SampleItem>>[
            const PopupMenuItem<SampleItem>(
              value: SampleItem.itemOne,
              child: Text('Item 1'),
            ),
            const PopupMenuItem<SampleItem>(
              value: SampleItem.itemTwo,
              child: Text('Item 2'),
            ),
            const PopupMenuDivider(),
            const CheckedPopupMenuItem<SampleItem>(
              value: SampleItem.itemThree,
              checked: true,
              child: Text('Item 3'),
            ),
          ],
        ),
      ),
    );
  }
}

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

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[QuncCccccc]

LGTM:) Just left one comment below. Thanks!