LibJS: Add the String.fromCodePoint() method

Author: https://github.com/IdanHo
Commit: 2299be474b
Pull-request: https://github.com/SerenityOS/serenity/pull/8081
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Tests/builtins/String/String.fromCodePoint.js

@@ -0,0 +1,37 @@
+test("basic functionality", () => {
+    expect(String.fromCodePoint).toHaveLength(1);
+
+    expect(String.fromCodePoint()).toBe("");
+    expect(String.fromCodePoint(0)).toBe("\u0000");
+    expect(String.fromCodePoint(false)).toBe("\u0000");
+    expect(String.fromCodePoint(null)).toBe("\u0000");
+    expect(String.fromCodePoint(1)).toBe("\u0001");
+    expect(String.fromCodePoint(true)).toBe("\u0001");
+    expect(String.fromCodePoint(0xffff)).toBe("\uffff");
+    expect(String.fromCodePoint(65)).toBe("A");
+    expect(String.fromCodePoint(65, 66, 67)).toBe("ABC");
+    expect(String.fromCodePoint(228, 246, 252)).toBe("äöü");
+});
+
+test("errors", () => {
+    expect(() => {
+        String.fromCodePoint(NaN);
+    }).toThrowWithMessage(
+        RangeError,
+        "must be an integer no less than 0 and no greater than 0x10FFFF"
+    );
+
+    expect(() => {
+        String.fromCodePoint(-5);
+    }).toThrowWithMessage(
+        RangeError,
+        "must be an integer no less than 0 and no greater than 0x10FFFF"
+    );
+
+    expect(() => {
+        String.fromCodePoint(0x123ffff);
+    }).toThrowWithMessage(
+        RangeError,
+        "must be an integer no less than 0 and no greater than 0x10FFFF"
+    );
+});