feat(lsp): multiple deno.json scopes

[nayeemrmn]

TODO:

• Remove remaining invocations of the ConfigTree::root_*() methods. This includes Documents resolver creation, setting and vendor dirs.
• Tests.
• Adjust specifier-enabled logic on the vscode_deno side. Will probably add a request for this to ask the server if a specifier is enabled instead of recreating the detection. Need to figure out how to integrate that.
• Rebase.

[bartlomieju]

@nayeemrmn something's gone wrong when merging with main, there's a ton of unrelated commits. Could you try rebasing it once again?

[nayeemrmn]

This project is complete as of #24345 landing