Make the alignment parameter optional when negotiating buffers.
Default to a 16 bytes alignment and adjust for the max cpu
alignment.
Remove the useless align buffer parameter in plugins, we always
set it to 16 anyway.
The posibility to drop single modifier was added in this development
circle (after 0.3.39 release). To have clients work with older versions
of PipeWire dropping all modifiers can be an option.
This commit uses the video-src-alloc and video-play-reneg templates to create
examples for manual fixation at the format negotiation phase. These
clients simulate modifier negotiation done by clients handling DmaBufs.
Note: Neither client is capable of proper DmaBuf handling!
video-play-fixate can be used to test if a producer is capable to
fallback to shm buffer transport, while video-src-fixate can only be
used with the former example!
