Increase VSE strip channels limit from 32 to 128
The original limit dates back from 2002 when Blender went open source.
After that many years some productions (e.g., Sprite Fright) are already
experiencing limitations for complex edits.
The future plans is to support an initial shorter (2?) number of
channels with support to "unlimited" channels.
Finally, I'm bumping the minimum file requirement since files with more
than 32 channels won't work well in old Blender versions.
In a future commit I will implement a sanitization so that we only read (and write)
128 channels. Making sure future changes of this number won't corrupt Blender.
Differential Revision: https://developer.blender.org/D12645