perf: Use === or Set.has instead of array.indexOf for keyword checks

packages/babel-parser/test/unit/util/identifier.js

@@ -0,0 +1,18 @@
+import { isKeyword } from "../../../src/util/identifier";
+
+describe("identifier", () => {
+  describe("isKeyword", () => {
+    it("break is a keyword", () => {
+      expect(isKeyword("break")).toBe(true);
+    });
+    it("let is a keyword", () => {
+      expect(isKeyword("let")).toBe(true);
+    });
+    it("super is a keyword", () => {
+      expect(isKeyword("super")).toBe(true);
+    });
+    it("abc is not a keyword", () => {
+      expect(isKeyword("abc")).toBe(false);
+    });
+  });
+});