* memory-manage images and shaders

__has_feature(cxx_rtti) is a clang extension, but clients of this code
are mostly using the VS toolchain. This makes the RTTI check work with
more compilers.

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