register ProgressNotifier service

[camilledejoye]

Depends on phpactor/language-server#36

It registers a new ProgressNotifier service which is responsible to send progress to the client using window/showMessage or $/progress depending on the client capabilities.

[dantleech]

Phpstan is failing, you could add a simple test to ensure that the service can be retrieved: https://github.com/phpactor/language-server-extension/blob/master/tests/LanguageServer/Unit/LanguageServerExtensionTest.php

[dantleech]

I'll fix it :)

[camilledejoye]

I think phpstan was failing because the dependency was not updated yet.
I didn't even thought of looking for a test, it's just simple configuration for me to setup a container.