Add thumb color customization to CupertinoSwitch

[sunyujia-rakuten]

Description

When using the CupertinoSwitch allow to set the thumb color.

This fixed the following issue: #86774

Tests

I added the following tests:

• A test which confirms that the CupertinoSwitch.thumbColor is set
• A test which confirms that the CupertinoSwitch.thumbColor is using default

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 feature I am adding, or Hixie said the PR is test-exempt.
• All existing and new tests are passing.

Breaking Change

Does your PR require Flutter developers to manually update their apps to accommodate your change?

• Yes, this is a breaking change (Please read Handling breaking changes). Replace this with a link to the e-mail where you asked for input on this proposed change.
• No, this is not a breaking change.

[skia-gold]

Gold has detected about 2 new digest(s) on patchset 1.
View them at https://flutter-gold.skia.org/cl/github/86775

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[LongCatIsLooong]

6a6c34d LGTM but you might need to remove the irrelevant commits.

[sunyujia-rakuten]

6a6c34d LGTM but you might need to remove the irrelevant commits.

yeah my bad

[LongCatIsLooong]

LGTM. Thanks for contributing!

[sunyujia-rakuten]

LGTM. Thanks for contributing!

Hi , @LongCatIsLooong . I don't remember when i requested a review from @jmagman for this PR . Is there anything else I need to do?

[jmagman]

Is there anything else I need to do?

This needed the waiting for tree to go green label added to merge. Added the label, should go once the tree reopens.

[sunyujia-rakuten]

This needed the waiting for tree to go green label added to merge. Added the label, should go once the tree reopens.

Okay，Thanks！