* Hint the VM when a layer or picture goes out of scope

Related issue: https://github.com/flutter/flutter/issues/56719

Fixes https://github.com/flutter/flutter/issues/59109

Fixes https://github.com/flutter/flutter/issues/53117

Test added:
- ShellTest.CanLoadSkSLsFromAsset

This reverts commit f6b8eda7.

This change also adds TimeRecorder which records time at the start
of each frame to capture the latest vsync target display time and
wires it in to the rasterizer to add trace events when there is a lag.

Fixes https://github.com/flutter/flutter/issues/53114

Also update all known test harnesses to use this and fixes the broken shell_unittests harness.

Fixes https://github.com/flutter/flutter/issues/49853

This paves the way for us to have shell_unittests backed by different rendering APIs (e.g. OpenGL, Vulkan, Metal).

This reverts commit 6ea69a0d.

On top of the revert, it reverted a commit in the PR:
https://github.com/flutter/engine/pull/14024

This reverts commit ea67e5b0b930ebf552bc7dbd678a35ee6a129c39.

This reverts commit d117ac97.

This makes it so that the platform views can be passed
an arbitraty CreateVsyncWaiter callback that lets us inject
a vsync waiter other than just the simulated monotonic vsync waiter
that currently exists.

This move makes it easier to add more vsync waiters.

* Remove erroneous ChildView opacity

* Wire frame metrics through contexts

* Maintain layer stack inside of SceneBuilder

* Remove EnsureSingleChild

* Centralize system-composite and elevation logic

* Wire up OpacityLayer to Scenic

* Revert "Add flow test fixtures and tests (#13986)"

This reverts commit 620f5281.

* Revert "Dynamically determine whether to use offscreen surface based on need (#13976)"

This reverts commit a86ef946.

* Moves pointer event sanitizing to engine

* fix comment format

* fix formatting

* addressing comment

* fix format

* fix format

* addressing comment

This reverts commit f456423c.

This is being reverted because it caused flutter/flutter#45098
(images don't load on iOS).

This reverts commit 2dcfaaeb.

This reverts commit 618e6666.

Revert "Always use `IOSGLContextSwitch` to access EAGLContexts to prevent plugins from polluting Flutter's EAGLContext (#13314)" (#13753)

Always use `IOSGLContextSwitch` to access EAGLContexts to prevent plugins from polluting Flutter's EAGLContext (#13314)

This re-enables thread safety checks for WeakPtr. WeakPtrs can't be used on a thread other than the one the WeakPtrFactory was created on.

This fixes the unit tests and adds a getUnsafe() method to WeakPtr to work around the remaining unresolved locations where we are using WeakPtr unsafely.

Fixes https://github.com/flutter/flutter/issues/42704.

For https://github.com/flutter/flutter/issues/40686

Unit tests added:
- CacheSkSLWorks
- VisitFilesCanBeCalledTwice
- CanListFilesRecursively

This reverts commit c2879cae.

Additionally, we fix https://github.com/flutter/flutter/issues/40863 by adding a secondary VSYNC callback.

Unit tests are updated to provide VSYNC mocking and check the fix of https://github.com/flutter/flutter/issues/40863.

The root cause of having https://github.com/flutter/flutter/issues/40863 is the false assumption that each input event must trigger a new frame. That was true in the framework PR https://github.com/flutter/flutter/pull/36616 because the input events there are all scrolling move events. When the PR was ported to the engine, we can no longer distinguish different types of events, and tap events may no longer trigger a new frame.

Therefore, this PR directly hooks into the `VsyncWaiter` and uses its (newly added) secondary callback to dispatch the pending input event.

* Add windows font change logic

* update

* fix comment

This reverts commit aac33d1b.

Reason: flutter/flutter#40863

TBR: chinmaygarde, iskakaushik

Additionally, we now use the engine directly as a delegate instead of storing potentially dead runtime_controller.

Unit tests have been updated to include an engine restart check which would fail before the fix.

This fixes https://github.com/flutter/flutter/issues/40303

This reverts commit b569e8c2.