feat: add intelephense support for php

[creativenull]

This PR will add initial support for intelephense for PHP.

I've added some tests to go with it. I've never done vim tests with vader before so I took inspiration from the tests implemented from test/command_callback/test_php_langserver_callbacks.vader file.

For the config options, I'm not too sure how I can check if initialization_options were properly read by intelephense. But I have only one test case for that, if someone knows how to do this I won't mind updating this PR with it.

[stale]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests.
If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[creativenull]

@w0rp @hsanson or any other maintainer out there to take a look at this? All checks are passed, I have couple tests added, unless more is needed.

[w0rp]

Cheers! 🍻