[look-controls] Support Pointer Lock API.

[donmccurdy]

Fixes #2625.

From the last comment:

Yeah, I'm in favor of a Pointer Lock on by default. I shared some A-Frame stuff to people on desktop and the click-drag is not usable. For default desktop mode, I'd favor Pointer Lock/a-cursor versus Click-Drag/mouse-cursor (they conflict anyways).

... it sounds like we're leaning toward "on by default" rather than "on by default after entering fullscreen". If that's still correct and we want to merge this, I'll add the tests and docs.

/cc @ngokevin

[dmarcos]

I personally think pointer lock feels too aggresive when in non VR mode. Specially when sharing the space with other 2D page elements like for instance the aframe.io website where the scenes are delivered via iframe or in the embedded use cases.

[donmccurdy]

The A-Frame website with a scene embedded in other 2D page content seems like the exception rather than the rule, and it can always be disabled... would you suggest other defaults? Default the option to off? Remove the option but automatically enable pointerlock in fullscreen mode?

It's a pretty significant usability improvement for more cases than not, in my opinion, so at least having the option on the table would be nice.

[ngokevin]

I still prefer defaulting it. Embedded cases seem like an exception to me too, and even then, the canvas is often still the focus of the page. With embedded sites, mouse-drag becomes more difficult to use because the canvas is a smaller click target to constantly aim back at after you drag away. When you click on the canvas, you intend to engage with it, so it's fine to me to provide Pointer Lock since it's easier to use.

[dmarcos]

Thanks!

[dmarcos]

It needs tests fixed

[donmccurdy]

Docs and tests added. ✅

[dmarcos]

Thanks!