Closes #139558

In this PR:

• Use <details open> to create opened collapsible sections (still be expanded if needed)
• Change checkboxes (at the top of the issue, namely I have searched the existing issues and I have read the guide to filing a bug) to text only.

Demo filed issues for opened collapsible sections

• I am having difficulty installing Flutter or getting it to work
• Report a bug
• Report a bug in one of Flutter's first-party packages
• My app is slow or missing frames
• My app has some non-speed performance issues

Demo for checkboxes to text

• I am having difficulty installing Flutter or getting it to work
• Report a bug
• Feature request
• The CI infrastructure used by Flutter has a problem
• Report a bug in one of Flutter's first-party packages

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.

If you need help, consider asking for advice on the #hackers-new channel on Discord.