Rework examples to use 0.10.0 polyfill

[jsantell]

Also fixes an issue with responding correctly to polyfilled vrdisplaypresentchange events, since the display property lives on a event.detail object due to CustomEvent restrictions. Tested on desktop and mobile with no API support, and on mobile with daydream support.

This is dependent on landing immersive-web/webvr-polyfill#298, but wanted to get this out for any changes needed before then.

functionality changes:

• due to the removal of the desktop VRDisplay, accessing these samples on a non-supported desktop correctly gives the "WebVR found but no display" messages.
• The test- samples had POLYFILL_MODE = 'always', which hasn't been an option in the polyfill for as long as I remember, so this currently isn't an option in the polyfill (can discuss adding it!), but the API will no longer always be clobbered. FWIW, the previous version of the polyfill in this repo didn't have the option implemented anyway, so no change 😄
• BUFFER_SCALE set to 0.75 in some demos. Sometime last year the default was reduced from 1.0 to 0.5. Just a note, not sure if this is necessary now with the lower default (and if the other samples should use 1.0)

[jsantell]

Just landed 0.10.0 changes FYI

[toji]

LGTM, thanks! I'm a fan of the newer syntax, BTW.

[jsantell]

Same! Smoothing out the path to WebXR Device API polyfill 😄