LibJS: Create the RegExpExec result's "input" field last

We move the input string into this field to avoid a string copy, so we
must do this step last to avoid using any views into it (note that
match.view here is a view into this string).

Userland/Libraries/LibJS/Tests/builtins/RegExp/RegExp.prototype.exec.js

@@ -205,3 +205,10 @@ test("multiline stateful match", () => {
     );
     expect(res.index).toBe(231);
 });
+
+test("string coercion", () => {
+    let result = /1/.exec(1);
+    expect(result.length).toBe(1);
+    expect(result[0]).toBe("1");
+    expect(result.index).toBe(0);
+});