Fix expanding bit depth in AVIF

[awxkee]

Rotate left replicates bits, with assumption that our data is 16 bit, by amount shifted left, so for 10 bit it shift left by 6 and it replicates 0 bits to the lower half, but we need 6.
Hence rotate left is (value << n) | (value >> (16 - n)) but we need (value << n) | (value >> (bit_depth - n)).

[RunDevelopment]

LGTM.

Using bitshifts only approximates a proper unorm conversion, but it should be good enough here. The conversion from 8 bits is exact, and the maximum absolute error for 10 and 12 bits is 1 bit (or $2^{-16}$).