## Description

As we've introduced offset to the Opacity layer, we have to override
`applyTransform` to make Leader/FollowerLayer work correctly.

## Related Issues

Fixes https://github.com/flutter/flutter/issues/30587

Together with https://github.com/flutter/engine/pull/8585,
this test will also exercise test against
https://github.com/flutter/flutter/issues/30586.

## Tests

I added the following tests:
* text field selection toolbar renders correctly inside opacity