fix(types): add Error.isError type (#28679)

cli/tsc/dts/lib.deno.unstable.d.ts

@@ -3746,3 +3746,14 @@ interface DataView {
    */
   setFloat16(byteOffset: number, value: number, littleEndian?: boolean): void;
 }
+
+/**
+ * @category Platform
+ * @experimental
+ */
+interface ErrorConstructor {
+  /**
+   * Indicates whether the argument provided is a built-in Error instance or not.
+   */
+  isError(error: unknown): error is Error;
+}