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 commitsda6d6f99a8,14b60c3a1c. This commit should tackle the remaining occurrences. Pull Request: blender/blender#106060