feat(affine-vscode): languageClientSendRequest host binding (Refs #103)

#103 slice-2 (sendRequest half — owner-scoped; the callback half is
tracked separately in #199).

Adds languageClientSendRequest to the VscodeLanguageClient binding map
in packages/affine-vscode/mod.js (the JS-side impl the #103 acceptance
criteria names). It reads the method + JSON params string, parses the
params (empty/malformed -> no params), invokes c.sendRequest, and
registers the returned Thenable in the handle table — matching the
existing newLanguageClient/start/stop pattern. No host->guest callback
involved, so it is unaffected by the Deno callback-ABI gap.

node --check clean. mod.js is a JS package (not dune-built); no 253
impact.

Pilot scope note: the rsr-certifier vscode extension calls sendRequest
*inside* a vscode.window.withProgress wrapper. withProgress needs the
host->guest callback ABI, which the source-to-source backend lacks
(#199). The full pilot restore is therefore blocked on #199; forcing a
withProgress-less partial rewrite of a cross-repo production extension
would be a damaging partial change and is deliberately not done here.
This PR delivers the enabling binding; the pilot follows #199.

Refs #103

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

packages/affine-vscode/mod.js

@@ -345,6 +345,27 @@ module.exports = function makeVscodeBindings(vscode, lcModule, hostShim) {
       if (c) c.stop();
       return 0;
     },
+    // `LanguageClient.sendRequest(method, params)` (issue #103). `params`
+    // arrives as a JSON string (the binding's synchronous extern shape);
+    // we parse it, invoke the LSP request, and register the returned
+    // Thenable in the handle table. The consumer awaits it on the
+    // source-to-source path (the wasm path additionally needs the
+    // thenable-resolution primitives — tracked in #199). An empty or
+    // malformed params string is treated as no params.
+    languageClientSendRequest: (cHandle, methodPtr, paramsJsonPtr) => {
+      const c = get(cHandle);
+      if (!c) return 0;
+      const method = readString(methodPtr);
+      const raw = readString(paramsJsonPtr);
+      let params;
+      if (raw && raw.length > 0) {
+        try { params = JSON.parse(raw); } catch (_e) { params = undefined; }
+      }
+      const thenable = params === undefined
+        ? c.sendRequest(method)
+        : c.sendRequest(method, params);
+      return reg(thenable);
+    },
   };
 
   return { Vscode, VscodeLanguageClient };