[LSP] Enable Pull Diagnostics

[dibarbet]

Top level issue to track enabling LSP pull diagnostics by default

Dogfood blocking issues

• [LSP] Support diagnostics requests for projection scenarios #58778 (external)
• De-dupe build diagnostics regression https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1552639/
• Diagnostic squiggles missing for project context scenarios in latest main
• Support diagnostics in additional files - Add support for additional file diagnostics in workspace pull #61930

Issues blocking turning on by default

• [External] (Request diagnostics at a slower rate from open non-visible documents) https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1569166
• [LSP] Diagnostics do not refresh on option change #62495
• [External] (Support interactive window / file rename) https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1563105
• [External] https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1569172 [LSP] Report syntax diagnostics from document pull without waiting for semantic diagnostics #62560
• [External] Workspace diagnostics requests cancelled after 2 minutes - https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1576626
• [External] Workspace diagnostics requests block text document diagnostics requests until workspace completes or is cancelled - https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1576625
• [External] Workspace diagnostics are not requested until a file is opened - https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1578505/
• The entire expression is faded when LSP pull diagnostics are on #63147

Non-blocking issues

• [LSP] Use frozen partial semantics for document pull diagnostics #61275
• Need to figure out how someone can configure suppressions from the error list if we don't own the error list.
• Need to remove IDiagnosticService.DiagnosticsUpdated. Currently this is used by tagger (but is not needed if tagger is just pulling), and by typescript. David believes TS just uses this for LSP-push-diags in liveshare and can likely be removed since we have worked with them to support pull diagnostics.
• Move IDiagnosticService.GetDiagnosticsAsync to be snapshot based. Currently it takes in Workspace+ProjId/DocId. This is non-sensical as that means you may get random results depending on the state of Workspace.CurrentSnapshot. This needs to move to take Project/Document instead.

See also: #62741, #62735 and #62771

Next steps

• Enable flag for team
• Rollout to internal preview users
• Rollout to external preview users
• Rollout to everyone

[CyrusNajmabadi]

I'm closing this out as pull diags has been on for ages. if there's more to do ehre, we can have targeted issues for that.