Generate Method code action

[BladeMF]

A code action for the "Generate method" refactoring. Some points (also noted in the code):

• It doesn't provide diagnostics (although the code is there, the tag is commented out from the container setup), because it doesn't check method calls for "undefined method". I wanted to push v1 out and mess around with (potentially) slow calls to Worse reflection for v2. So the whenever the code for provideDiagnostics is fitted with "check for undefined method", it will be good to go;
• As a result, if a method is defined and the code action is executed, nothing happens;
• It shows up on all method calls;
• Otherwise it's really nice to use.

The test I intentionally made a unit test rather than an integration test, because:

• Integration tests are really complicated to setup and I rather not do this without a reason;
• A single integration case for a CodeActionProvider and DiagnosticsProvider will prove the plumbing is working - I'd rather test each CodeActionProvider whether they provide the correct actions/diagnostics in the correct context and then test whether the Command is passing to and from the model and handling exceptions.

The only problem with the above is the very difficult mocking of the ClientApi class. We can create a ClientApiSpy class that collects all calls to public function request(string $method, array $params): Promise and public function notification(string $method, array $params): void methods or allows a callback to emulate responses.

[BladeMF]

Not sure why 7.3 CS fixer fails...

[dantleech]

restarted the build, probably temporary failure. you should be able to use the LS server tester more than you have, but it's already much better by using RpcTestClient.

[dantleech]

:boom: I will see if I can iterate on this for diagnostics and the tests.