feat: restart server command in vscode

[Eric-Song-Nop]

The upstream bugs might crash the language server in many cases, I feel it a requirement to have an explicit way to restart the language server client in such case.

[Myriad-Dreamin]

Some thoughts:

• We could detect and restart the server once after user editing typst document. It is not done intermediately after server down, to avoid infinite or aggressively restart.
• The right-below status bar could hints the user that currently the server is down for some reason, e.g. "Crashed", hovering with message "Compiler panicked: blabla".

[Myriad-Dreamin]

I refactored code to help ensure that all resources are disposed when deactivating the extension. Otherwise we'll not be able to restart reliably. It is better to separate a PR, but we can also merge the two commits in this PR if we both are lazy.