ruff server: Support publish diagnostics as a fallback when pull diagnostics aren't supported (#11092)

## Summary

Fixes #11059 

Several major editors don't support [pull
diagnostics](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_pullDiagnostics),
a method of sending diagnostics to the client that was introduced in
version `0.3.17` of the specification. Until now, `ruff server` has only
used pull diagnostics, which resulted in diagnostics not being available
on Neovim and Helix, which don't support pull diagnostics yet (though
Neovim `10.0` will have support for this).

`ruff server` will now utilize the older method of sending diagnostics,
known as 'publish diagnostics', when pull diagnostics aren't supported
by the client. This involves re-linting a document every time it is
opened or modified, and then sending the diagnostics generated from that
lint to the client via the `textDocument/publishDiagnostics`
notification.

## Test Plan

The easiest way to test that this PR works is to check if diagnostics
show up on Neovim `<=0.9`.

crates/ruff_server/src/server/api/diagnostics.rs

@@ -0,0 +1,34 @@
+use crate::{server::client::Notifier, session::DocumentSnapshot};
+
+use super::LSPResult;
+
+pub(super) fn generate_diagnostics(snapshot: &DocumentSnapshot) -> Vec<lsp_types::Diagnostic> {
+    if snapshot.client_settings().lint() {
+        crate::lint::check(
+            snapshot.document(),
+            &snapshot.settings().linter,
+            snapshot.encoding(),
+        )
+    } else {
+        vec![]
+    }
+}
+
+pub(super) fn publish_diagnostics_for_document(
+    snapshot: &DocumentSnapshot,
+    notifier: &Notifier,
+) -> crate::server::Result<()> {
+    let diagnostics = generate_diagnostics(snapshot);
+
+    notifier
+        .notify::<lsp_types::notification::PublishDiagnostics>(
+            lsp_types::PublishDiagnosticsParams {
+                uri: snapshot.url().clone(),
+                diagnostics,
+                version: Some(snapshot.document().version()),
+            },
+        )
+        .with_failure_code(lsp_server::ErrorCode::InternalError)?;
+
+    Ok(())
+}