Integrate Pigeon for Android #340

Job	Run time
Build Android example app (stable channel)	2m 42s
Build iOS example app (3.19)	1m 15s
Build Android example app (3.19)	2m 8s
Run Dart Analyzer	56s
Build iOS example app (stable channel)	1m 22s
Build Linux example app (stable channel)	1m 9s
Build macOS example app (3.19)	1m 19s
Build macOS example app (stable channel)	1m 29s
Dart formatting checks	25s
Build Linux example app (3.19)	45s
Build Windows example app (3.19)	2m 15s
Build Windows example app (stable channel)	2m 39s
Run integration tests (Android)	2m 44s
Run integration tests (iOS)	2m 56s
Run all unit tests (Android)	2m 52s
Run all unit tests except for Windows (Dart)	1m 7s
Run Windows unit tests (Dart)	2m 39s
	30m 42s

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