emscripten: keep track of pointer lock losses and maybe regrab pointer later.

If an Emscripten app is in relative mouse mode and the user presses Escape
(or whatever is appropriate), then the pointer lock is broken by the browser.

This keeps track of those losses, and next time the user presses a mouse
button down on the canvas, if the app is still meant to be in relative mouse
mode, we will attempt to regrab the pointer.

This makes it much more seamless for things like first-person shooters, and
the app doesn't need any manual intervention.

extra : rebase_source : 182fa61448b455cd4f9108746be61d936ef5efcc
2 files changed