Fixes several bugs in the clipboard code, and makes some structural
improvements:
- Adds scoped wrappers for clipboard open/close and global lock/unlock,
  to prevent missing cleanup, fixing at least one case where the lock
  was not released.
- Adds the relevant window handle to the clipboard calls, since the docs
  suggest that some operations won't work without one.
- Adds a missing clear step to setting the clipboard data.
- Switches from TEXT to UNICODETEXT to handle non-ASCII text correctly.
  - To enable that, adds UTF-16/-8 conversion utilities built on the
    Win32 APIs (rather than the deprecated std::codecvt functions, as
    have been previously used in the engine).
- Fixes handling of getting data when the clipboard is empty, correctly
  returning null.
- Passes more errors back through the method channel, with details, for
  easier debugging of future issues.

Fixes https://github.com/flutter/flutter/issues/54226

reduce web shard count from 8 to 4 by using WEB_SHARD_COUNT

* store paint command bounds
* do not apply commands outside the clip region
* better cull rect prediction
* enforce RecordingCanvas.endRecording

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/fuchsia-linux-sdk-flutter-engine
Please CC  on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

* Updates to use predefined keys.

It starts using:
  * timeouts for paving.
  * timeouts for ssh commands.
  * timeouts for tests.

https://github.com/flutter/flutter/issues/54416

* Update key location and autogenerate public key.

* Use ssh-keygen instead of openssl.

* Fix typo on test name.

Desktop embedding dependencies can trigger gn-generation-time
requiremenets; e.g., the Linux embeddings have pkg-config dependencies.
This can be problematic in some build environments, such as building
flutter_engine.so with a custom sysroot where those higher-level
dependencies aren't available.

This flag allows generating build files that don't have those
dependencies.

* Fix extra canvas generation due to context access
* add comment
* address review comment

- Adds an explicit option for not building the GLFW embedding.
- Disables GLFW by default on Windows, where it's no longer the
  uploaded embedding.
- Moves the X11 pkg-config, which is only used by the GLFW embedding,
  behind the GLFW build flag.

Update docstrings for typos and grammar style specified in the style guide.

* Add test and dartfmt
* Update golden locks
* Addressed review comments
* Fix lint error (unused widthConstraint)
* Add maxDiffRatePercent for text diff on mac/linux

* changing felt script to fetch flutter

* changing the clone_flutter.sh code

* running integration tests with felt on cirrus. fetch framework in CI (not in local).

* only run cirrus tests on chrome. fix a comma in the flutter command path

* adding comments to public flags

* use local engine parameter for flutter pub get

* change flutter executable used for flutter drive command

* fix a cleanup issue. address comments. add toolException. enable web in flutter

* address reviwer comments. fix issue with local-engine

* address reviwer comments. fix issue with local-engine

* using engine/flutter/.dart_tools as clone directory. enabling clone script for local usage

* clean flutter repo with felt clean. add a flag to skip cloning the repo. always clone the repo even for local development, unless this flag is set

* fixing typos. updating readme for the new flag.

* fix directory error

* addressing reviewer comments