Previously the group-tab extended all the way down to the
last track. Potentially with a widget height of > 2^15 px.
This caused issues with gtk widgets (notably on Windows)
```
unhandled exception (type std::exception) in signal handler:
what: invalid value (typically too big) for the size of the input (surface, pattern, etc.)
```
This also prepares for Mixer Tab-Group to use the same
separation between visible and total extent.
a menu allows choosing between all markers or 1 specific type, and all ranges or 1 specific type
more work required on menu structure and menu options/dialogs to specify the type of new location
and range marker creation
The suspend/resume routes code requires that there be a call to
Editor::redisplay_track_views() if anything is to happen on resume. This was
missing from the events triggered by a UI scale change.
Deleting _track_canvas_viewport automatically destroys
any child Items. The LocationMarker's group was already destroyed
when ~ArdourMarker() runs and calls `delete group`.
So first delete the marker, then the canvas
* in the 'fake_drag' case (dragging the playhead from the ruler), the
mouse events are delivered to the playhead during the drag so we need
to temporarily sensitize the playhead during that operation, then reset
the sensitivity via config
This is mostly a simple lexical search+replace but the absence of operator< for
std::weak_ptr<T> leads to some complications, particularly with Evoral::Sequence
and ExportPortChannel.
Import via Drag/Drop previously worked by selecting a track,
and then importing to the selected track.
This approach fails when the selected track is in a track-group,
and selecting the track also selects other tracks of different type.
Now the track to drop onto is passed directly passed through to
::finish_bringing_in_material as existing_track.
The track-header (gtk) is packed with 1px box spacing. This
is added at the top of each box (best seen by looking at the
group-tab vs track-header alignment in the editor).
However the actual track separator line on the canvas is at the
bottom of each track, aligning with the top of the next track
or automation-lane.
The first track however lacks a separator at the top, which
needs to be provided by the ruler. Once the canvas is scrolled
this ruler/canvas separator overlaps with the bottom separator of
each TAV.
Using ruler Rectangle::set_outline had various issues.
The outline extends outside the rectangle. It bled into the
video-timeline instead of the canvas' top y-axis pixel.
Also the separator was above the video-timeline, not above the
canvas. Hence a dedicated separator Line is preferable.
It also provides a consistent separator if no rulers are visible.
