LSP: Implement diagnostics

[phated]

Problem

The LSP should implement diagnostics (compilation & type checking error messages/warnings/etc) following https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_diagnostic

This could be implemented as "publish" (via the server) or "pull" via the client, see https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_publishDiagnostics and https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_pullDiagnostics respectively.

We likely also want to implement workspace diagnostics as per https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#workspace_diagnostic (see "Implementation Considerations" at the bottom)

Happy Case

Users should receive feedback on the state of the code they write via an LSP client. This can include red or yellow underlines for errors and warnings or other feedback they need.

Alternatives Considered

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

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