Part of work on [#101077](https://github.com/flutter/flutter/pull/141194). This is done as a separate PR to avoid a massive diff.

## Context
1. The `FakeCommand` class accepts a list of patterns that's used to match a command given to its `FakeProcessManager`. Since `FakeCommand` can match a list of patterns, not just specifically strings, it can be used to match commands where the exact value of some arguments can't (easily) known ahead of time. For example, a part of the tool may invoke a command with an argument that is the path of a temporarily file that has a randomly-generated basename.
2. The `FakeCommand` class provides on `onRun` parameter, which is a callback that is run when the `FakeProcessManager` runs a command that matches the `FakeCommand` in question.

## Issue
In the event that a `FakeCommand` is constructed using patterns, the test code can't know the exact values used for arguments in the command. This PR proposes changing the type of `onRun` from `VoidCallback?` to `void Function(List<String>)?`. When run, the value `List<String>` parameter will be the full command that the `FakeCommand` matched.

Example:
```dart
FakeCommand(
  command: <Pattern>[
    artifacts.getArtifactPath(Artifact.engineDartBinary),
    'run',
    'vector_graphics_compiler',
    RegExp(r'--input=/.*\.temp'),
    RegExp(r'--output=/.*\.temp'),
  ],
  onRun: (List<String> command) {
    final outputPath = (() { 
      // code to parse `--output` from `command`
    })();
    testFileSystem.file(outputPath).createSync(recursive: true);
  },
)
```