LibJS: ArrayBuffer.prototype.slice

Implements the aforementioned native Javascript function, following the
specification's [1] implementation.

[1] https://tc39.es/ecma262/#sec-arraybuffer.prototype.slice

Userland/Libraries/LibJS/Tests/builtins/ArrayBuffer/ArrayBuffer.prototype.slice.js

@@ -0,0 +1,29 @@
+test("single parameter", () => {
+    const buffer = new ArrayBuffer(16);
+    const fullView = new Int32Array(buffer);
+
+    // modify some value that we can check in the sliced buffer
+    fullView[3] = 7;
+
+    // slice the buffer and use a new int32 view to perform basic checks
+    const slicedBuffer = buffer.slice(12);
+    const slicedView = new Int32Array(slicedBuffer);
+
+    expect(slicedView).toHaveLength(1);
+    expect(slicedView[0]).toBe(7);
+});
+
+test("both parameters", () => {
+    const buffer = new ArrayBuffer(16);
+    const fullView = new Int32Array(buffer);
+
+    // modify some value that we can check in the sliced buffer
+    fullView[1] = 12;
+
+    // slice the buffer and use a new int32 view to perform basic checks
+    const slicedBuffer = buffer.slice(4, 8);
+    const slicedView = new Int32Array(slicedBuffer);
+
+    expect(slicedView).toHaveLength(1);
+    expect(slicedView[0]).toBe(12);
+});