When the `Join` operator was added to Grease Pencil v3 the behavior when
joining points was changed. The selected point would now be split from the
existing strokes and put into a new one.
This behavior is often undesirable, leading to multiple user reporting it as a
bug #130293, #141368, #131036, #132201, #136144 and #144300.
This PR adds a new mode, `Join Strokes` that behaves the same as legacy
grease pencil, and sets it as default. This PR also renames the existing modes
to `SplitAndCopy`, `SplitPoints` to better indicate the expected behavior.
Pull Request: https://projects.blender.org/blender/blender/pulls/144666
fad44198a3