Fix internal document link handling

[DaelonSuzuka]

This PR adds a DocumentLinkProvider that creates internal hyperlinks for all res://path/to/file.ext strings in gdresource files.

Additionally, this provides a workaround for the Language Server's broken behavior of sending invalid file URIs in Godot 3. I tested the workaround with both the current broken 3.5stable LSP and the fixed version that I created a PR for. The same fix is already implemented in master, so that means this workaround should also work correctly with Godot 4.

Code_lKEInQAWaF.mp4

The technique used for this workaround could be useful for mitigating other defects in the Language Server, like fixing bad completions(#152, #189) or suppressing incorrect errors(#280, #266),

[Calinou]

Should be good to merge after following suggestions.

[Calinou]

Thanks!