Fix theme updating when VS Code auto theme detection is on

[kv9898]

Fixes #861

I admit the fix is a bit ugly and I wish better solutions are possible.

[vezwork]

Thanks so much for the PR @kv9898 !

I am not working on theme-related stuff right now, but I will be, hopefully before the end of the year. I will come back to review your PR then. I will try to help come up with a clean solution to the problem.

[kv9898]

Thanks so much for the PR @kv9898 !

I am not working on theme-related stuff right now, but I will be, hopefully before the end of the year. I will come back to review your PR then. I will try to help come up with a clean solution to the problem.

Thanks! I understand that Quarto is highly modularized and communication between parts can be tricky (and debugging quarto is definitely not easy from my experience).

[kv9898]

@vezwork Happy New Year! Any updates?

[vezwork]

Tried this out and it does seem to fix the issue.

I looked into the solution and it does seem that:

1. using vscode.window.activeColorTheme.kind with onDidChangeActiveColorTheme is a good way to get the actual current theme kind
2. you cannot directly access the theme kind in the LSP, so you have to send a message from the HOST.
3. We don't currently exactly have a precedent for sending messages from the HOST to the LSP (-- don't have a precedent for sending data, we do send requests in custom.ts, maybe we should use that instead?). See:

   quarto/apps/overview.md

   Lines 67 to 68 in 326b1e0

   	- EXTENSION HOST <-req-- LSP
   	- I don't think this happens?

   
   so it seems reasonable to use the notification messaging functionality of the LSP.

As such, this was pretty close to a minimal solution. I cleaned it up a bit. It is also a necessary fix in other ways because our colorTheme config in the LSP did not accurately represent the current theme previously, it only represented the user's colorTheme setting.

[juliasilge]

Thank you for working on this!