Work towards https://github.com/dart-lang/linter/issues/4859

There are libraries outside a `lib/` directory, which violate `implementation_imports`.

Supersedes https://github.com/flutter/flutter/pull/143560.

Related to tracker issue:
- https://github.com/flutter/flutter/issues/128251

This updates the `Analytics` constructor to provide it with the enabled features for the flutter-tool. This will be sent with each event for the flutter-tool.

Related to the tracker issue:
- https://github.com/flutter/flutter/issues/128251

This PR migrates the `Usage.command` static method that sent custom dimensions for each command (if applicable). The screenshot below shows the different places where the `usageValues` getter is overwritten to return the necessary custom dimensions for that command.

<img width="285" alt="image" src="https://github.com/flutter/flutter/assets/42216813/e32d5100-0e17-4a4d-8f21-327a8c113a19">

Relanding based on this comment:
- https://github.com/flutter/flutter/pull/139278#issuecomment-1832951108

Related to tracker issue:
- https://github.com/flutter/flutter/issues/128251

<img width="278" alt="image" src="https://github.com/flutter/flutter/assets/42216813/cee7b9be-48d6-48e5-8c39-de28d0a1f0de">

The image above shows all of the instances where we have `sendTiming`. All of the call sites have been updated to use the new `Event.timing` event from `package:unified_analytics`.

Reverts flutter/flutter#138896
Initiated by: CaseyHillers
This change reverts the following previous change:
Original Description:
Related to tracker issue:
- https://github.com/flutter/flutter/issues/128251

<img width="278" alt="image" src="https://github.com/flutter/flutter/assets/42216813/cee7b9be-48d6-48e5-8c39-de28d0a1f0de">

The image above shows all of the instances where we have `sendTiming`. All of the call sites have been updated to use the new `Event.timing` event from `package:unified_analytics`.

Related to tracker issue:
- https://github.com/flutter/flutter/issues/128251

<img width="278" alt="image" src="https://github.com/flutter/flutter/assets/42216813/cee7b9be-48d6-48e5-8c39-de28d0a1f0de">

The image above shows all of the instances where we have `sendTiming`. All of the call sites have been updated to use the new `Event.timing` event from `package:unified_analytics`.

Fixes issues:
- https://github.com/flutter/flutter/issues/138035

Similar to GA3, we will now record the host running the flutter tool, such as VSCode, stored in the `FLUTTER_HOST` env variable

Fixes https://github.com/flutter/flutter/issues/136698.

Alters how `throwToolExit` creates its matcher. This results is an improved description of the matcher.

The mismatch description isn't improved by this, but I writing an entirely custom matcher to fix this isn't ideal either. We can instead mitigate the issue by augmenting the `toString` implementation of `ToolExit` to include the exit code, if it is non-null.

With these changes, the first few lines of output from a test would look like this:

```
Expected: throws <Instance of 'ToolExit'> with `exitCode`: <42> and `message`: contains 'message'
  Actual: <Closure: () => Never>
   Which: threw ToolExit:<Exit code: 41232. Error: message>
```

Related to tracking issue:
- https://github.com/flutter/flutter/issues/128251

This PR sends analytic events for each of the doctor validators.

This PR below will need to land first in `dart-lang/tools` before this merges.

Fixes https://github.com/flutter/flutter/issues/133086

Most of these imports were never appropriate. The `test_api` package was never intended for use in `_test.dart` files.
Where possible move imports to `matcher`, otherwise move them to `test` or `flutter_test`.

Leave uses of `test_api` from `flutter_test` library code.

Remove 1745 decorative breaks

Co-authored-by: Enguerrand_ARMINJON_MAC_2 <earminjon@sqli.com>

This reverts commit cb378edc.

* Flutter_tools for web platform: report error messages with stacks on toolExit

Print error messages and stacks in verbose mode before calling
`throwToolExit` on communication errors to chrome and dwds.

This will help us disagnose CI flakes:

Helps: https://github.com/flutter/flutter/issues/84012
Closes: https://github.com/flutter/flutter/issues/87149

* Added tests

* Extend timeout for testing failure to connect to chrome

* Update rest of chrome tests to await until matching is finished

This reverts commit 0cbe5975.

* opt out the flutter tool

* oops EOF

* fix import

* Update tool_backend.dart

* Update daemon_client.dart

* fix more