This PR addresses Issue number: 163840, where when hovering over a Cupertino button the mouse cursor wouldn't switch to clickable and there wasn't any option to configure it.

Adds Mouse cursor to CupertinoButton, CupertinoButton.Filled and CupertinoButton.Tinted

Fixes #163840
Part of #58192

Demo of the changes

Code snippet showing new behavior

import 'package:flutter/cupertino.dart';

void main() => runApp(
  // const Center(child: Text('Hello, world!', key: Key('title'), textDirection: TextDirection.ltr)),
  CupertinoApp(
    theme: const CupertinoThemeData(
      brightness: Brightness.light,
    ),
    home: Center(
      child: Column(
        spacing: 5.0,
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: <Widget>[
          CupertinoButton(
            onPressed: (){},
            child: const Text('Default Cursor'),
          ),
          CupertinoButton(
            onPressed: (){},
            mouseCursor: SystemMouseCursors.grab,
            child: const Text('Custom Cursor'),
          ),
          CupertinoButton.filled(
            onPressed: (){},
            mouseCursor: SystemMouseCursors.copy,
            child: const Text('Custom Cursor 2'),
          ),
          CupertinoButton.tinted(
            onPressed: (){},
            mouseCursor: SystemMouseCursors.help,
            child: const Text('Custom Cursor 2'),
          ),
        ],
      )
    ),
  ),
);

List which issues are fixed by this PR. You must list at least one issue. An issue is not required if the PR fixes something trivial like a typo.

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

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.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

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