Expose bits_per_coded_sample on VideoCodecContext

[rvanlaar]

qtrle decoder needs bits_per_coded_sample to be set when decoding a packet.

[jlaine]

Can we have a unit test which exercises the getter and setter please?

[WyattBlue]

In addition to jlaine's comments, this needs to be redone with the new style property attribute and it needs the type hint.