LibJS: Hook up Regex<ECMA262> to RegExpObject and implement `test()'

This makes RegExpObject compile and store a Regex<ECMA262>, adds
all flag-related properties, and implements `RegExpPrototype.test()`
(complete with 'lastIndex' support) :^)
It should be noted that this only implements `test()' using the builtin
`exec()'.

Libraries/LibJS/Tests/builtins/RegExp/RegExp.prototype.test.js

@@ -0,0 +1,58 @@
+test("basic functionality", () => {
+    expect(RegExp.prototype.test).toHaveLength(1);
+});
+
+test("simple test", () => {
+    let re = /test/;
+    expect(re.test("test")).toBe(true);
+    expect(re.test("test")).toBe(true);
+});
+
+test("simple global test", () => {
+    let re = /test/g;
+    expect(re.test("testtest")).toBe(true);
+    expect(re.test("testtest")).toBe(true);
+    expect(re.test("testtest")).toBe(false);
+    expect(re.test("testtest")).toBe(true);
+    expect(re.test("testtest")).toBe(true);
+});
+
+test("global test with offset lastIndex", () => {
+    let re = /test/g;
+    re.lastIndex = 2;
+    expect(re.test("testtest")).toBe(true);
+    expect(re.test("testtest")).toBe(false);
+    expect(re.test("testtest")).toBe(true);
+    expect(re.test("testtest")).toBe(true);
+    expect(re.test("testtest")).toBe(false);
+});
+
+test("sticky test with offset lastIndex", () => {
+    let re = /test/y;
+    re.lastIndex = 2;
+    expect(re.test("aatest")).toBe(true);
+    expect(re.test("aatest")).toBe(false);
+    expect(re.test("aatest")).toBe(false);
+});
+
+test("flag and options", () => {
+    expect(/foo/gi.flags).toBe("gi");
+    expect(/foo/mu.flags).toBe("mu");
+    expect(/foo/gimsuy.flags).toBe("gimsuy");
+
+    let re = /foo/gim;
+    expect(re.dotAll).toBe(false);
+    expect(re.global).toBe(true);
+    expect(re.ignoreCase).toBe(true);
+    expect(re.multiline).toBe(true);
+    expect(re.sticky).toBe(false);
+    expect(re.unicode).toBe(false);
+
+    expect(() => {
+        /foo/gg;
+    }).toThrowWithMessage(SyntaxError, "Repeated RegExp flag 'g'");
+
+    expect(() => {
+        /foo/x;
+    }).toThrowWithMessage(SyntaxError, "Invalid RegExp flag 'x'");
+});