Doc Improvements

[Piinks]

Description

Came across some issues that turned out to be opportunities for better docs.

Related Issues

Fixes #17090
Fixes #12033
Fixes #39715

Tests

N/A

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.

[goderbauer]

LGTM

Always good to see improvements to the docs! Thanks.

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite hostonly_devicelab_tests-0-linux has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite hostonly_devicelab_tests-2-linux has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite hostonly_devicelab_tests-3_last-linux has failed. Please fix the issues identified (or deflake) before re-applying this label.
• The status or check suite firebase_test_lab_tests-linux has failed. Please fix the issues identified (or deflake) before re-applying this label.