*now that you can grab "anywhere" in the region, trim edges are inferior because they are hard to hit
*modifier had to change anyway (since CTRL is used as a copy-drag on both mac and win), so that invalidates prior muscle memory
*potentially frees up modifier on the trim edge for some other purpose (anchored_trim)
Control Points should ignore x_constraint which is set in Drag::motion and potentially other places.
The only thing that should prevent CP sliding is can_slide which is false for the points at the ends of a region.
Ripple edit undo/redo needs a "recursive diff" of all regions
in the playlist. To work properly owned changes have to be
cleared first, previously unrelated edits were be collected too.
This includes a more consistent version of
7a89d56009 using rdiff() instead of explicitly
saving region diffs.
Previously x-axis threshold was in samples. This is
useless unless zoomed in to the max. So in most cases
the first-move was always in x-direction, making constrained
y-axis drags near impossible.
Furthermore the threshold for copy-drags was increased
as per #8686
Region positions were updated in the GUI, before the playlist
was catching up.
The butler thread reads a region using the region's new position,
but the playlist's old range.
Thread 1 (GUI)
```
#22 ARDOUR::Playlist::notify_layering_changed()
#26 ARDOUR::AudioPlaylist::region_changed
#27 ARDOUR::Playlist::region_changed_proxy
#35 ARDOUR::Region::send_change
#36 ARDOUR::Region::set_position
#37 RegionRippleDrag::remove_unselected_from_views
#38 RegionRippleDrag::finished
```
LayeringChanged() also triggers DiskIOProcessor::playlist_modified
which schedules a pending-override and summons the butler.
Note that when moving only a few regions the butler starts after all
updates have been completed.
Butler thread:
```
#4 ARDOUR::AudioRegion::read_at
#5 ARDOUR::AudioPlaylist::read
#6 ARDOUR::DiskReader::audio_read
#7 ARDOUR::DiskReader::overwrite_existing_audio
#8 ARDOUR::DiskReader::overwrite_existing_buffers
#9 ARDOUR::Track::overwrite_existing_buffers
#10 ARDOUR::Session::non_realtime_overwrite
```
Region read fails:
```
libs/ardour/audioregion.cc:503 assert (position >= _position);
(gdb) p position
$1 = 1312000
(gdb) p _position
$2 = {<PBD::PropertyTemplate<long>> = {_have_old = true,
_current = 1336000, _old = 1312000} }
```
The DraggingView's time_axis_view (index) is set to the size of _time_axis_views
in ::motion() near line 1149. This makes it invalid as index into the vector.
