Move findExecutable to extension host

Part of #101073

src/vs/workbench/api/browser/mainThreadTask.ts

@@ -668,6 +668,9 @@ export class MainThreadTask implements MainThreadTaskShape {
 			},
 			getDefaultShellAndArgs: (): Promise<{ shell: string, args: string[] | string | undefined }> => {
 				return Promise.resolve(this._proxy.$getDefaultShellAndArgs());
+			},
+			findExecutable: (command: string, cwd?: string, paths?: string[]): Promise<string | undefined> => {
+				return this._proxy.$findExecutable(command, cwd, paths);
 			}
 		});
 	}