Functions formerly in ardour/util.h and some more functions.
The main motivation is libevoral which can use libpbd but not libardour.
The eventual goal is to consolidate various different interpolation,
scaling and deflection methods.
Trim automation is planned via SlavableAC as normal AutomationMode.
Some of this code have a revival (a special "Trim+Preview" state
before merging Automation but that has to be more general than Pan & Gain.
The first click to select a new stripable may actually un-select strip.
counting and ignoring this leads to strange behavior.
Also when the selection_counter hit zero, VCAs were not ignored.
whatever this workaround was good for, it's more trouble than it's worth.
As side-effect this also improves DnD + Gtk::Entry behavior with stock GTK.
Remove old code to remove duplicate engine state which was used to
work-around a bug since 3.x saved duplicates but broke with 4.x separate
i/o devices.
Add a new variant to purge old unused states per backend (after sorting).
* add an abstract StripableTimeAxisView (Route TAV + VCA TAV)
* move common strip-methods into STAV
* Add Automation Lanes to VCA TAV
* Allow ATAV without Automatable for VCA Controls
Cloning a region retains the region-lock style.
Playlist partitioning set the region start-property only (audio-time).
If a MIDI region is locked to musical-time, Properties::start is ignored
and overwritten by Properties::start_beats.
* The UI and ctrl-surface controls use and display the combined value,
including control-masters.
* The Automation lane of a control is the raw value of the control
without masters.
When touching (or writing) automation, the control-master needs to be
factored out (or subtracted). e.g press+hold a control -> write inverse
master automation.
This went unnoticed because: VCA gain automation was always applied
(regardless of automation state) but when it was not playing
master_ratio() factored it out again (per block).
