ee-wayland: use frame callbacks exclusively to determine render timing

ee-wayland: use frame callbacks exclusively to determine render timing

when running in a wayland compositor, the ideal mode of operation is to
only prepare/send frames when the compositor has finished with the previous
frame

to achieve this, manual rendering can be toggled upon creating and completing
a frame callback, ensuring that a canvas never has multiple pending buffers at
any given time

fix T2784