In most common cases, an Pointer or Collection rna property needs a
custom liboverride 'apply' callback, if it supports modifying or adding
data in liboverrides.
The main change in this commit is that diffing code won't generate
anymore operations that are not supported on such properties.
In addition, the check on such invalid operations at liboverride apply
time has been turned into a `CLOG_ERROR` message, instead of an assert.
This is both more visible (as it also prints in release builds), and
less critical (as it won't terminate blender execution).
e2f83dd267