feat: add GlobalLspListener

[rchl]

I've been thinking a bit on how to support support sublimelsp/LSP-volar#221

My latest idea is to not do any magic to make LSP-typescript initialize for Vue files and instead when LSP-volar is initialized on a vue file, and LSP-typescript is not running, add a Phantom at the top of the file that tells the user to initialize LSP-typescript to get the full experience. Clicking on the phantom triggers a window command that modifies project settings that enables LSP-typescript for Vue files and also enables the vue plugin by referencing it from the LSP-volar storage path. Would look something like:

To implement that idea I need some global listener that will tell me whenever a session initializes or shuts down on a view thus this API. It would be used like this:

from LSP.plugin import GlobalLspListener
from LSP.plugin import Session
from LSP.plugin import windows

class SessionListener(GlobalLspListener):

    def __init__(self) -> None:
        self._phantoms: dict[int, sublime.PhantomSet] = dict()

    def on_session_initialized_async(self, view_listener: AbstractViewListener, session: Session) -> None:
        pass

    def on_session_shutdown_async(self, view_listener: AbstractViewListener, session: Session) -> None:
        pass


session_listener = SessionListener()


def plugin_loaded():
    LspVolarPlugin.setup()
    windows.add_global_listener(session_listener)


def plugin_unloaded():
    windows.remove_global_listener(session_listener)
    LspVolarPlugin.cleanup()

Let me know if you have any better idea on how this could be handled.