This allows metas to be serialized to be transmitted or stored. This is
intended to be used for example by gdppay or unixfdsink.
Implemented on GstCustomMeta, GstVideoMeta, GstReferenceTimestampMeta,
and GstAudioMeta.
Sponsored-by: Netflix Inc.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5355>
When the alignment contains nothing, all its fields are 0 and always
can be satisfied. So there is no need to validate it in this case.
And there are a lot of places just setting this alignment to default
all zero value, this validation generates lots of warnings.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4674>