Add Lua LSP integration support

[SalHe]

Hi!
I like Mesen very much. I have added LSP integration in script editor for type annotation and other support. Due to some restriction, I just reimplement the code completion and hove tips in editor. And add code for downloading LSP server automatically(I am not sure whether it's acceptable for you).

Changes mainly for:

1. Type annotation except getState/setState (they diff from situation and may be unstable, so I just annotate it with table), with type annotation meta file we can code in external editor with code completion and etc.
2. Mouse hover tips.
3. Completions on entering (not only for .).
4. Download LSP Server automatically (Test passed on Windows-x64).

There may be more works to improve the editor experience:

1. Code format.
2. Error lens. (I didn't find relative approach to represent error within AvaloniaEdit.TextEditor in place)
3. Images in completion.
4. Improve completing
5. Config for LSP Client.
6. Whether to embed a LSP server?

Here is a picture for illustrating: