This specific option type is only used for the video aspect. The
underlying type was a float to represent the inputted value, but it's
actually not precise enough. When using something like 4:3, the values
of the incorrect digits are actually significant enough to make av_d2q
return a very funky numerator and denominator which is close to 4/3 but
not quite. This leads to some "off by one pixel" errors. Weirdly, mpv's
actual calculations for this were already being done as double, but then
converted to floats for this specific type. Just drop the conversion
step and leave it all as double which has the precision we need (i.e.
AVRational is now 4/3 for the this case). Fixes#8190.