SimpleDialogOption: support custom padding

[arthurdenner]

Description

This PR adds support for a custom padding property on SimpleDialogOption. After running the Accessibility Scanner on one of my apps, I was pointed that the height of the options should be bigger, but there is no current support for that and I extended the SimpleDialogOption class to add it. Now, I'm proposing this change to be added on Flutter itself.

Related Issues

I couldn't find any.

Tests

I added the following tests:

• Custom padding on SimpleDialogOption

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read Handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change. If not, delete the remainder of this section.

[shihaohong]

Also, it seems like the flutter analyzer is failing on trailing whitespace. Also, unrelated presubmit checks are failing to you might have to rebase with upstream/master

[shihaohong]

LGTM, minus the typo in the API doc

[shihaohong]

Thank you for your contribution, it has just been merged :)

[arthurdenner]

Thank you for the reviews and interactions here, @shihaohong!