A buffer is a technical term most often referred to using the metaphor
of a "clipboard" in applications. However, the "clipboard" is usually
the system clipboard, used to carry data accross applications. To
avoid confusion, this replaces "clipboard" by "internal clipboard"
when not dealing with the system clipboard.
In addition, a few places still used the "[copy/paste] buffer"
terminology, so they are replaced with "internal clipboard as well.
The replacement from "[copy/paste] buffer" to "clipboard" was
undertaken in previous commits da6d6f99a8, 14b60c3a1c. This
commit should tackle the remaining occurrences.
Pull Request: https://projects.blender.org/blender/blender/pulls/106060
84e216fcee