Bug 1542808 - Implement widget-local VsyncSource for Wayland windows. r=stransky,lsalzman

Lets Wayland sessions run vsync off wayland surface frame callbacks by creating
an interface for widgets to return a local VsyncSource, if applicable.

This interface is currently used for the compositor, and for refresh drivers
in the parent process. It is not yet used for vsync in content processes.

Differential Revision: https://phabricator.services.mozilla.com/D28430

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extra : moz-landing-system : lando