Bundle all tests into a single app binary

[bartekpacia]

We want to fix flutter/flutter#115751 in Patrol, and (hopefully) upstream it to Flutter.

The idea and implementation is described in-depth in flutter/flutter#115751 (comment) and flutter/flutter#115751 (comment).

Tasks:

• Fully migrate native reporting to use gRPC #969
• Generate artificial bundle test that references all tests #1025
• Replicate Dart tests on Android - crucial #1026
• Replicate Dart tests on iOS - crucial #1027
• Clean up test bundling implementation #1214
  • Discuss implementation with the Technical Advisory Board, make sure than breaking changes are necessary
  • Test bundling clean up - remove possibility to run on many devices #1316
• Bring back patrol develop - done in Bring back Hot Restart #1286

Additionaly:

• Display nice summary in the console after running tests #1028 (tentative: 2.0 or 2.1)

Except from being a significant speedup (from $O(n)$ to $O(1)$ in build time), it'll also solve:

• better test reports (currently results from each Dart file end up in a separate report)
• test sharding

[bartekpacia]

Important caveats

General

• cannot use setUp(), setUpAll(), tearDown(), tearDownAll()
• cannot use group()

iOS

• Running on physical iOS has problems
• App data is not cleared between test runs on iOS #1317

[bartekpacia]

Problems, bugs, and shortcuts taken should be documented in #1341.

[github-actions]

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