This patch defaults the volatility bit on SkPaths to false, and then flips it to true if the path survives at least two frames.

Switch the MacOS Desktop embedder to using a thread configuration where the platform and render task runners are the same. (#13300)

Also creates a new test harness for the desktop embedder framework target and adds a test that launches a headless engine in this new thread configuration.

Fixes https://github.com/flutter/flutter/issues/17579

* Make test Dart2 compliant

* Use service and debug events instead of polling to wait for isolate to start, run and resume.

* Refactor into _onServiceEvent. Wait for 'paused' event instead of 'isolate runnable'.

* Namespaces have been updated to reflect the move from //flutter/sky/shell to //flutter/shell.
* shell/BUILD.gn file has been split into smaller GN files for each subcomponent of the shell (common, GPU, diagnostic, testing).
* GN dependencies have been rewritten to stop exposing common shell dependencies as public. Duplicates have also been removed.
* GPU subcomponent has been updated make it more suitable for Vulkan integration.
* The GLFW backend has been resurrected.

Example:
  JavaClass dateFormatClass = Java.getClass('java.text.SimpleDateFormat');
  JavaObject format = dateFormatClass.newInstance('yyyy.MM.dd');
  print(format.parse('2016.01.01').getYear());

* Conversion of all primitive types, wrapped Java objects, and nulls between Dart and Java
* A way to distinguish float arguments from doubles when calling Java methods
* Construction of a Dart JniClass from a Java class object

Also adopt a standard pattern for handling exceptions in JNI APIs

This also extends DartClassLibrary to support multiple DartClassProviders
for different libraries