TS: Added VRButton.d.ts.

examples/jsm/webxr/VRButton.d.ts

+import {
+	WebGLRenderer
+} from '../../../src/Three';
+
+export interface WebXROptions {
+	referenceSpaceType: string;
+}
+
+export namespace VRButton {
+	export function createButton( renderer: WebGLRenderer, options?: WebXROptions  ): HTMLElement;
+}