lsp doesn't respect deno.unstable (on startup)

[irbull]

While investigating (#21159) is seems there is another case where the LSP doesn't respect the unstable flag. This is unrelated to the /// <reference no-default-lib="true" /> directive.

Steps to reproduce:

1. Start a new instance of VSCode
2. Initialize a Deno workspace (with unstable API)
3. Create a file with the following Deno.dlopen and save it
4. It will complain that dlopen is an unstable API.

If you restart the LSP, the setting sticks. Seems like a timing issue on startup.

I've attached a screengrab.

[irbull]

I spent some time today with both the LSP server and the VSCode extension looking at this issue. Here is what seems to be happening:

1. When you Initialize the Deno Workspace 3 things are set (deno.enable, deno.lint & deno.unstable).
2. These are set sequentially through await config.update
3. The first of these deno.enable causes the LSP to restart
4. When the other settings are applied, the update_tsconfig is not called
5. If you change the settings file manually, it will be picked up by the filewatcher.

[irbull]

Opps, sorry @nayeemrmn I missed that you had a PR here when I commented. Yes, that looks right. I pulled it down and it fixes the issue.

I'm not sure I understand the changes to the tests and how they relate to this issue, but I'll leave a comment on the PR about that.