Record, move recorded region(s), delete the recorded source, undo.
Undo would undo the region-move, of a region that no longer
exists and has no source.
This fixes the following issue:
1. Import a file to a new track
2. Delete the track
3. Editor Source list: select imported file,
-> Remove the selected source
-> Yes, remove the Regions and Sources
The Track and Region no longer exist in the Editor,
only the playlist still exists!
The sources to be deleted are found when iterating over whole-file
regions in `EditorSources::remove_selected_sources`. Also
RegionFactory::get_regions_using_source correctly returns
regions, _editor->remove_regions does nothing since there
is no RegionView for the given region(s). This then cashes in
```
libs/ardour/playlist.cc:2400: virtual XMLNode& ARDOUR::Playlist::state(bool) const: Assertion `r->sources ().size () > 0 && r->master_sources ().size () > 0' failed.
```
The eventual goal is to keep the set of used regions
in sync, and allow to remove explicit calls to
`sync_all_regions_with_regions`.
This prevents `all_regions` to retain a reference to
a region that has been destroyed.
* Do not emit signal with source-lock mutex held
* explicitly drop references when called directly; notably from
EditorSources::remove_selected_sources
This will allow PBD::Filearchive to properly report progress.
It is also a generally useful API and deserves to be in libpbd.
Temporarily keep Ardour::Progress as alias
Despite the names suggesting otherwise
`block_notifications` and `ignore_state_changes` are used
for the same purpose.
The only difference is that ::freeze ::thaw explicitly
modified `ignore_state_changes` **in addition** to
`block_notifications`.
