This is part of a larger effort to expose the difference between GrDirectContext,
which runs on the GPU thread and can directly perform operations like uploading
textures, and GrRecordingContext, which can only queue up work to be delivered
to the GrDirectContext later.
This moves the Metal `GrContext` creation utilities from `GPUSurfaceMetal` into
a separate `IOSContext` object subclass. An analogue of this object was used in
the GL regime for the management of onscreen and offscreen contexts that were
not tied to the lifecycle of the `GPUSurface`. This pattern has now been
generalized for use with all backends that need a resource context
(`IOSContextGL` and `IOContextMetal`).
The platform views controller management in the `ExternalViewEmbedder` interface
implementation was repeated three times for [Metal][metal], [OpenGL](opengl) and
[Software](software) rendering. This repetition has been removed and a single
implementation present in the base `IOSSurface` and used on all platforms.
Addition of new client rendering APIs should not affect how the engine renders
into the platform view interleaving levels.
All rendering API selection logic has been moved into a single set of utilities
in `rendering_api_selection.h`. This enables the removal of a lot of code blocks
guarded by `FLUTTER_SHELL_ENABLE_METAL`. The remaining uses of this will be
removed when unified builds are enabled.
The Metal backend now also adds traces similar to the GL backend.
The `IOGLContext` has been renamed to `IOContextGL` to be more in line with the
convention used in this library.
Fixes https://github.com/flutter/flutter/issues/41827
Adds https://github.com/flutter/flutter/issues/52150
[metal]: 1194ba2b21/shell/platform/darwin/ios/ios_surface_metal.mm (L55)
[opengl]: 1194ba2b21/shell/platform/darwin/ios/ios_surface_gl.mm (L95)
[software]: 1194ba2b21/shell/platform/darwin/ios/ios_surface_software.mm (L146)
* Revert "Add flow test fixtures and tests (#13986)"
This reverts commit 620f5281b819f304e8e9e945222e26b17b087cc3.
* Revert "Dynamically determine whether to use offscreen surface based on need (#13976)"
This reverts commit a86ef946563b020108320bbfb974bf7343284fd3.
This reverts commit f456423cfb820d07bb36e9a8979e3d75cc9d8d76.
This is being reverted because it caused flutter/flutter#45098
(images don't load on iOS).
