LibWeb: Implement Element.innerText

Reading the property has a few warts (see FIXMEs in the included
tests), but with this the timestamps on http://45.33.8.238/
get localized :^)

Since the Date() constructor currently ignores all arguments,
they don't get localized correctly but are all set to the current
time, but hey, it's still progress from a certain point of view.

Libraries/LibWeb/Tests/DOM/Element.js

@@ -0,0 +1,24 @@
+loadPage("file:///res/html/misc/innertext_textcontent.html");
+
+afterInitialPageLoad(() => {
+    test("Element.innerText", () => {
+        var p = document.getElementsByTagName("p")[0];
+        expect(p.innerText).toBe("This is a very small test page :^)");
+
+        // FIXME: Call this on p once that's supported.
+        var b = document.getElementsByTagName("b")[0];
+        b.innerText = "foo";
+        expect(b.innerText).toBe("foo");
+        expect(p.innerText).toBe("This is a foo test page :^)");
+
+        p.innerText = "bar";
+        expect(p.innerText).toBe("bar");
+
+        var p = document.getElementById("source");
+        // FIXME: The leading and trailing two spaces each are wrong.
+        // FIXME: The text should be affected by the text-transform:uppercase.
+        expect(p.innerText).toBe(`  Take a look at
+how this text
+is interpreted below.  `);
+    });
+});