This improves raster cache control from apps and enables
GPU acceleration for some offscreen workloads that would
fallback to software.

Test: PlatformViewTests.GetGrContextTest
Co-authored-by: NDavid Reveman <reveman@google.com>

* Fix nullability warning and change registeredFonts to non-nullable
* Renamed var

* Sync verb enum to skia. Fix PathIterator.peek, add tests
* Add constant for iterator buffer size

Co-authored-by: NKaushik Iska <kaushikiska@google.com>

New command for Crowdsource 2/2

This change creates the scenic session with request to Focuser. The
focuser is used to request focus to a view, given it's ViewRef. The call to
requestFocus is made from PlatformView messages channel, which will
be used from Flutter side by ChildView.

Adds a PlatformView unittest for the requestFocus method.
Co-authored-by: NSanjay Chouksey <sanjayc@google.com>

Remove the gni file, as it is confusing things

Standard*Codec allows for extensions to support arbitrary types; this
had not previously been implemented for the C++ version.

Overview of changes:
- EncodableValue's std::variant type now allows for a new CustomEncodableValue, which is a thin wrapper around std::any, to store arbitrary extension types.
- ByteBufferStream* has been split into an interface class and the buffer-based implementation, with the former now part of the public API surface to be used in standard codec extensions.
  - They also gained utility methods for some common data types to simplify writing extensions.
- StandardCodecSerializer is now part of the public API surface, and is subclassable.
- StandardCodecSerializer's ReadValue has been split into ReadValue and ReadValueOfType to match the structure used when subclassing on the Dart side, for easier porting of custom extensions across languages.
- Standard*Codec now optionally accepts a non-default serializer in GetInstance, providing a shared instance using that serializer.

Fixes https://github.com/flutter/flutter/issues/31174

This fixes lint errors in the vulkan directory. This might be a little more controversial, but the reason that the lints were failing here was because of an include path problem that I think I solved.

Changes the interaction between the view controller and engine in both the C API and
the engine API, so that there's always an engine (as on other platforms) rather than
the engine APIs being specific to headless mode.

While adjusting the C API, this does a large cleanup:
- Renames all methods to follow a `FlutterDesktop` (prefix) + "class" name + method-style name.
  E.g., `FlutterDestkopViewControllerCreate` rather than `FlutterDesktopCreateViewController`.
  This makes it easier to see what functions operate on which conceptual "object" in the API.
- Reorders and groups them by the object they operate on.

Fixes https://github.com/flutter/flutter/issues/61966