presentation-time: bump protocol version to v2

We've actually been doing the wrong thing this whole time, for v1 of the protocol, we should set the refresh_nsec field to 0 if the output does not have a constant refresh rate. However we've been setting it to the fastest rate instead since eac7c2ad which is incidentally exactly what v2 of the protocol proposes.

So allow advertising v2, and fix v1 to set refresh_nsec to 0.

wlr_presentation_create now takes a version param.

sway patch: https://github.com/swaywm/sway/pull/8389