Allows mouse clicks to be used for selection with Windows Mixed Reality Headsets in Edge

Summary:
Adds support for Windows Mixed Reality mouse input by responding to pointer restriction events
When pointer is restricted, the only way to recieve mouse clicks is via pointerLock
Release pointerlock when not restricted to enable demo driver type scenarios

## Motivation (required)

Allows mouse clicks to be used for selection with Windows Mixed Reality Headsets in Edge

## Test Plan (required)

Load any React-based WebVR experience in Microsoft Edge, enter VR, and ensure mouse clicks function to select and click on 3D objects
Press Win+Y and ensure pointerlock is released and the mouse moves freely on the desktop
Closes facebookarchive#328

Differential Revision: D5819876

Pulled By: andrewimm

fbshipit-source-id: 5f6a94f

Author: Nell Waliczek (HOFFMAN)

OVRUI/src/Player/Player.js

@@ -186,6 +186,8 @@ export default class Player {
     (this: any).handleFullscreenChange = this.handleFullscreenChange.bind(this);
     (this: any).exitVR = this.exitVR.bind(this);
     (this: any).resetAngles = this.resetAngles.bind(this);
+    (this: any).handlePointerRestricted = this.handlePointerRestricted.bind(this);
+    (this: any).handlePointerUnrestricted = this.handlePointerUnrestricted.bind(this);
 
     this.isMobile = isMobile;
     this.allowCarmelDeeplink = !!options.allowCarmelDeeplink && isSamsung;
@@ -365,11 +367,37 @@ export default class Player {
     // Listen for headsets that connect / disconnect after the page has loaded
     window.addEventListener('vrdisplayconnect', this.onDisplayConnect);
     window.addEventListener('vrdisplaydisconnect', this.onDisplayDisconnect);
+    // Listen for pointer becoming restricted / unrestricted
+    window.addEventListener('vrdisplaypointerrestricted', this.handlePointerRestricted);
+    window.addEventListener('vrdisplaypointerunrestricted', this.handlePointerUnrestricted);
 
     // Detect any VR displays, so that we can pick the proper rAF and render
     this.initializeDisplay();
   }
 
+  /**
+   * Handles taking ponterlock in response to pointer input being restricted
+   */
+  handlePointerRestricted() {
+    const pointerLockElement = this.glRenderer.domElement;
+    if (pointerLockElement && typeof(pointerLockElement.requestPointerLock) === 'function') {
+      pointerLockElement.requestPointerLock();
+    }
+  }
+
+  /**
+   * Handles releasing ponterlock in response to pointer input being unrestricted
+   */
+  handlePointerUnrestricted() {
+    // $FlowFixMe
+    const currentPointerLockElement = document.pointerLockElement;
+    const expectedPointerLockElement = this.glRenderer.domElement;
+    if (currentPointerLockElement && currentPointerLockElement === expectedPointerLockElement
+      && typeof(document.exitPointerLock) === 'function') {
+      document.exitPointerLock();
+    }
+  }
+
   /**
    * When WebGL is unsupported or disabled, render an error message.
    * @param width - The width of the parent container