Expose ProjectService to plugins (#23824)

Add refreshDiagnostics() method to Project

src/server/editorServices.ts

@@ -577,7 +577,8 @@ namespace ts.server {
             return this.pendingProjectUpdates.has(project.getProjectName());
         }
 
-        private sendProjectsUpdatedInBackgroundEvent() {
+        /* @internal */
+        sendProjectsUpdatedInBackgroundEvent() {
             if (!this.eventHandler) {
                 return;
             }

src/server/project.ts

@@ -164,7 +164,7 @@ namespace ts.server {
             return hasOneOrMoreJsAndNoTsFiles(this);
         }
 
-        public static resolveModule(moduleName: string, initialDir: string, host: ServerHost, log: (message: string) => void): {} {
+        public static resolveModule(moduleName: string, initialDir: string, host: ServerHost, log: (message: string) => void): {} | undefined {
             const resolvedPath = normalizeSlashes(host.resolvePath(combinePaths(initialDir, "node_modules")));
             log(`Loading ${moduleName} from ${initialDir} (resolved to ${resolvedPath})`);
             const result = host.require(resolvedPath, moduleName);
@@ -1102,6 +1102,11 @@ namespace ts.server {
             }
         }
 
+        /** Starts a new check for diagnostics. Call this if some file has updated that would cause diagnostics to be changed. */
+        refreshDiagnostics() {
+            this.projectService.sendProjectsUpdatedInBackgroundEvent();
+        }
+
         private enableProxy(pluginModuleFactory: PluginModuleFactory, configEntry: PluginImport) {
             try {
                 if (typeof pluginModuleFactory !== "function") {