This is plumbed through a new VOCTRL, VOCTRL_PERFORMANCE_DATA, and
exposed as properties render-time-last, render-time-avg etc.
All of these numbers are in microseconds, which gives a good precision
range when just outputting them via show-text. (Lua scripts can
obviously still do their own formatting etc.)
Signed-off-by: wm4 <wm4@nowhere>