Clean up on Pixel Streaming session disconnect

[hmuurine]

Summary

The Pixel Streaming library should clean up after it has finished a session. This helps integrating the lib within a single-page-app like a React app, where you might have the user navigate from a Pixel Streaming view to other views without a page refresh.

The current code leaves e.g. dangling event handlers connected to videoParent and document element, which it should clean up when not required any more. One of the symptoms of these dangling event handlers is a lot of console logging after disconnected whenever mouse or keyboard events are emitted:

This PR performs the following clean up tasks when the library has closed the session:

• Unregister all user input event handlers when disconnecting
  • These are registered again always on reconnecting, so it makes it symmetric if unregistering on disconnecting
• Use clearTimeout, not clearInterval to clear AFK timeout since it's not an interval
  • (actually in some browsers clearInterval accidentally clears also timeouts if called with a timeout id because of underlying implementation details, but this is not something guaranteed for all browsers)
• Added exitPointerLock() call to pointer lock mouse handler teardown
  • Exits pointer lock when disconnecting, but also if the lock happens to be active when some external API call toggles mouse input off or switches to hovering mouse event handler
• Also made pixelStreaming.disconnect() more robust by adding undefined checks
  • It previously crashed if disconnect() was called before connection was established. Got hit by this when implementing a test React app if navigating quickly out of the Pixel Streaming view before the connection was fully up

Test Plan

AFK timetout

• Opened a Pixel Streaming session with AFK timeout enabled
• Disconnected the UE app before the AFK timeout was triggered
• Waited and verified that the timeout was not triggered after disconnected

Unregister event handlers on disconnecting

• Opened a Pixel Streaming session in uiless.html

• Listed the event handlers connected to videoParentElement and document, and saw a bunch of event handlers
  

• Used the API to auto-disconnect after 10 seconds
  

• After disconnected listed the event handlers again and verified that all had been cleared
  

• Moved mouse around and pressed keyboard keys. Verified that there were no more console messages printed by the event handlers

• Retested the above by disconnecting from UE side, not through API. Verified that the event handlers were cleared also on UE side disconnect

• Used player.html to verify that disconnecting & reconnecting multiple times re-established the event handlers every time the connection was established. Verified that user input worked as expected after multiple reconnections

Pointer lock

• Opened a Pixel Streaming session with pointer lock mouse handler
• Clicked the video to lock mouse cursor
• Disconnected the UE app to trigger disconnect actions
• Verified that the pointer lock was released when disconnecting

[lukehb]

lgtm!