Closes https://github.com/flutter/flutter/issues/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](https://github.com/huycozy/flutter/issues/8)
- [Report a bug](https://github.com/huycozy/flutter/issues/9)
- [Report a bug in one of Flutter's first-party packages](https://github.com/huycozy/flutter/issues/11)
- [My app is slow or missing frames](https://github.com/huycozy/flutter/issues/12)
- [My app has some non-speed performance issues](https://github.com/huycozy/flutter/issues/10) 

### Demo for `checkboxes to text`

![Screenshot 2023-12-14 at 17 54 44](https://github.com/flutter/flutter/assets/104349824/1472b3bf-6245-4ec9-b7e8-d7ddf3d5a579)

- [I am having difficulty installing Flutter or getting it to work](https://github.com/huycozy/flutter/issues/new?assignees=&labels=&projects=&template=1_activation.yml)
- [Report a bug](https://github.com/huycozy/flutter/issues/new?assignees=&labels=&projects=&template=2_bug.yml)
- [Feature request](https://github.com/huycozy/flutter/issues/new?assignees=&labels=&projects=&template=3_feature_request.yml)
- [The CI infrastructure used by Flutter has a problem](https://github.com/huycozy/flutter/issues/new?assignees=&labels=team-infra&projects=&template=6_infrastructure.yml)
- [Report a bug in one of Flutter's first-party packages](https://github.com/huycozy/flutter/issues/new?assignees=&labels=&projects=&template=9_first_party_packages.yml)