Support for `workspace/diagnostic` from LSP 3.17

[versecafe]

Tracking issue for support on the LSP workspace/diagnostics request. Getting this working would be a major win over typescript-language-server and vtsls to get project wide diagnostics in editors where all issues are detected before each individual file is open the current reliance on didOpen makes editor workspace diagnostics less reliable.

[jakebailey]

I think this is something we want to do as a proper replacement to the (long experimental) typescript.tsserver.experimental.enableProjectDiagnostics setting, yes. It's certainly good that this is built-into the LSP as a request-based system, as opposed to us having to do this via push diagnostics (which we do not support outside providing diagnostics in tsconfig files).