Overflow handling works with clipping, adding an ellipsis on the last
line, or fading the last line.

Fixes https://github.com/flutter/flutter/issues/7271

fixes #7433

Skia calls this BlendMode now and that's a better name.

Fixes #7200

* s/sky/flutter/ in Android templates

* update engine.version with a compatible engine version

* replace more SkyActivity references with FlutterActivity

* Rollback commits to get iOS into a stable state

This rolls back the following commits:
* 23c52fc7 (#6434)
* a97cf4b5 (#6433)
* e72e1744 (#6428)

It also updates the engine to a newer revision that has the
necessary rollbacks in the engine repo.

Fixes #6458