The descriptions can change between different versions of the analyzer.

Speedup coverage test runs by using (new) coverage handle with caching.

On a `flutter test --coverage` run on `packages/flutter` the runtime goes from ~828 seconds to ~617 seconds, or a ~25% reduction in time spent (testing without coverage takes ~236 seconds so the overhead of `--coverage` in this case goes from ~592 seconds to ~381 seconds, or a ~35% reduction).

* Make deltas fail loudly

* analyzer fixes

* empty

* updates

* Analyzer fixes

* Make it more obvious what kind of TextRange is failing and where

* update tests

* Add tests for concrete TextEditinDelta apply method

* trailing spaces

* address nits

* fix analyzer
Co-authored-by: Renzo Olivares <roliv@google.com>