[tool] Wire dependency injection into runner and executable with required non-nullable contexts (#190922)

## Summary

Part 2 of the modular dependency injection migration (stacked on
#190724).

Wires explicit dependency injection into the Flutter tool entrypoints:
- Wires `ToolDependencies.bootstrap` into `runner.dart` to initialize
dependencies at startup.
- Updates `FlutterCommandRunner` to accept non-nullable `toolContext`,
`androidContext`, `appleContext`, and `toolDependencies`.
- Updates `executable.dart` to forward `ToolDependencies` into
`generateCommands`.
- Updates `test_flutter_command_runner.dart` and hermetic test doubles.

Part of https://github.com/flutter/flutter/issues/47161