Move Path and PathMetrics from canvas.dart into their own files. No delta (flutter#13772)

* Move Path and PathMetrics into their own files. No delta
* update file list in licenses_flutter

Author: ferhatb

ci/licenses_golden/licenses_flutter

@@ -446,6 +446,8 @@ FILE: ../../../flutter/lib/web_ui/lib/src/ui/initialization.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/ui/lerp.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/ui/natives.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/ui/painting.dart
+FILE: ../../../flutter/lib/web_ui/lib/src/ui/path.dart
+FILE: ../../../flutter/lib/web_ui/lib/src/ui/path_metrics.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/ui/pointer.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/ui/semantics.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/ui/test_embedding.dart