[Impeller] Fill/StrokePathGeometry use geom objects as path sources (#168125)

When basic rendering operations end up in a "general case" situation in
Impeller, it converts the basic shape into a path and calls `DrawPath`.
But, the creation of the path is expensive and all the mechanisms behind
drawing a path now only need a `PathSource` object which can replay the
path to them.

We now have explicit lightweight path source generators which can feed
the path drawing operations directly from the source data without having
to create a full `impeller::Path` object.
https://dart.googlesource.com/external/github.com/flutter/flutter/+/619c02f2a02f1834939df67728bfa1eb0dd939ff

DEPS

diff --git a/DEPS b/DEPS
index 6865d8f..1e66757 100644
--- a/DEPS
+++ b/DEPS
@@ -236,7 +236,7 @@
 deps = {
   'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'ba40d9bece5d59f8a40e9c5db4184213a3c071fa',
 
-  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + 'bc0d3289cb2cb6bcef303b5f99e6fa1aa3cf9fab',
+  'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '619c02f2a02f1834939df67728bfa1eb0dd939ff',
 
   'flutter/engine/src/flutter/third_party/depot_tools':
   Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '580b4ff3f5cd0dcaa2eacda28cefe0f45320e8f7',

commits.json

diff --git a/commits.json b/commits.json
index 6837725..df062a4 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
-  "flutter":"bc0d3289cb2cb6bcef303b5f99e6fa1aa3cf9fab",
+  "flutter":"619c02f2a02f1834939df67728bfa1eb0dd939ff",
   "flutter/engine/src/flutter/third_party/dart":"ba40d9bece5d59f8a40e9c5db4184213a3c071fa"
 }
\ No newline at end of file