## Description
This PR attemps to clarify the `InputDecoration.collapsed` documentation by explaining that it is not meant to be use with helper, label, counter, icons, prefixes and suffixes.
It also adds some parameters that make sense for a collapsed decoration (`hintMaxLines`, `hintFadeDuration`, `constraints`).
Removing parameters that should not have been added (`floatingLabelBehavior` and `floatingLabelAlignment`) will be part of another PR as it will require deprecations.
## Related Issue
Fixes https://github.com/flutter/flutter/issues/61331
## Tests
Adds 3 tests.