There are some inconsistencies and anachronisms in the various READMEs and in the API docs. This PR attempts to address them.
- Makes sure to link to platform-specific READMEs from the main README file.
- Makes the READMEs more consistent (e.g. only leaving the bare minimum quick start for the main README, and leaving all platform-specific notes to platform READMEs).
- Using the more correct “Not supported on all platforms” instead of “Supported on Android only” for functionality that works on both Android and the Web. Intentionally staying vague in API docs in order to make later maintenance easier. (https://github.com/flutter/flutter/issues/161948#issuecomment-2605429688)
- Remove a doc comment from before null safety about asserting non-null.
- Format the platform sections in the main README so that they’re proper lists, and so that all of them end with a link to the appropriate platform-specific README.
Issues:
- Fixes flutter/flutter#161954
- Related: flutter/flutter#161950, flutter/flutter#161948