WIP TextField prefix/suffix events - #38722

Description

In both Material and Cupertino, taps on a prefix or suffix in a text field are received by the text field itself as well as the prefix/suffix. This causes unexpected behavior when a button is in the prefix/suffix or even exceptions when clearing text.

The root cause of this problem is TextSelectionGestureDetector, which allows listening to all events, not just events given to it by the gesture arena. This is necessary, however, because it needs to listen to gestures that happen on top of the selection handles.

Cupertino Solution

CupertinoTextField already solves this problem for its built-in clear button. It uses a GlobalKey to check if a tap hits the clear button and ignores the tap if so. I've taken the same approach to solve this for prefix/suffix.

I added two parameters to enable this solution. Here is a typical use case:

CupertinoTextField(
  prefix: IconButton(...),
  prefixGesturesIgnored: true,
  suffix: IconButton(...),
  suffixGesturesIgnored: true,
)

Read more in the code and docs here.

Material Solution

This is still a work in progress. I'm trying to take the same approach, but prefix and suffix are passed into InputDecoration, so I can't directly give them GlobalKeys and access them in TextField's TextSelectionGestureDetector. I'm trying to work around that.

Related Issues

#36324
#39376
Closes #39376

Tests

TODO