feat: add TextAccessor, deprecate `.text()` as method (#32441)
Adds backward compat for `.text()` on messages while keeping `.text`
access
_The kicker:_
Any previous use of `.text()` will now need a `# type: ignore[operator]`
to silence type checkers. However, it will still behave as expected at
runtime. Deprecating in v0.4.0, to be removed in v2.0.0.