Fix VsyncWaiter (flutter#25551)

This PR accomplishes many things:
- Unblocks input resampling on Fuchsia
- Fixes 2 frame scheduling issues resulting in wasted work and missed frames
- Removes the now-defunct VsyncRecorder class
- Prepares the VsyncWaiter class for the Embedder API by moving all logic out of it
- Adds hundreds of lines of unittests for Fuchsia scheduling logic to validate the performance and correctness benefits

Author: farchond

ci/licenses_golden/licenses_flutter

@@ -1374,11 +1374,8 @@ FILE: ../../../flutter/shell/platform/fuchsia/flutter/task_runner_adapter.h
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/thread.cc
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/thread.h
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/unique_fdio_ns.h
-FILE: ../../../flutter/shell/platform/fuchsia/flutter/vsync_recorder.cc
-FILE: ../../../flutter/shell/platform/fuchsia/flutter/vsync_recorder.h
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/vsync_waiter.cc
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/vsync_waiter.h
-FILE: ../../../flutter/shell/platform/fuchsia/flutter/vsync_waiter_unittests.cc
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/vulkan_surface.cc
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/vulkan_surface.h
 FILE: ../../../flutter/shell/platform/fuchsia/flutter/vulkan_surface_pool.cc

shell/common/animator.cc

@@ -130,6 +130,7 @@ void Animator::BeginFrame(
       // If we still don't have valid continuation, the pipeline is currently
       // full because the consumer is being too slow. Try again at the next
       // frame interval.
+      TRACE_EVENT0("flutter", "PipelineFull");
       RequestFrame();
       return;
     }

shell/platform/fuchsia/flutter/BUILD.gn

@@ -83,8 +83,6 @@ template("runner_sources") {
       "thread.cc",
       "thread.h",
       "unique_fdio_ns.h",
-      "vsync_recorder.cc",
-      "vsync_recorder.h",
       "vsync_waiter.cc",
       "vsync_waiter.h",
       "vulkan_surface.cc",
@@ -455,8 +453,6 @@ executable("flutter_runner_unittests") {
     "runner_unittest.cc",
     "tests/engine_unittests.cc",
     "tests/flutter_runner_product_configuration_unittests.cc",
-    "tests/vsync_recorder_unittests.cc",
-    "vsync_waiter_unittests.cc",
   ]
 
   # This is needed for //third_party/googletest for linking zircon symbols.