Beatloop size: keep loop end, adjust loop start in UI by right-clicking on up/down buttons?

[mxmilkiib]

Feature Description

One can adjust the loop-out marker forwards and back by left clicking on the up and down arrows next to the size number.

How about moving the loop in marker back and forth by right clicking the same buttons?

Instead of showing a right-click context menu.

This would allow for more creative opportinuties.

[ronso0]

Sounds reasonable.

Note for all those who want to tackle this:
IMO squeezing this into WBeatSpinBox (used for both beatloop_size and beatjump_size) is rather complex since it can't be done with how the size control value change is currently transmitted to LoopingControl.
First obstacle: both button up/down clicks and Up/Down keyboard presses call WBeatSpinBox::stepBy, there one would somehow need to check if Shift is pressed.
Second, LoopingControl would need to know about "keep loop end position".

IMO, in order to make this available both in the GUI and for other controls (controllers) we need to

• create loop_halve/double_keep_end controls
• create separate Halve/Double buttons next to the spinbox
• hide the spinbox' up/down buttons with setButtonSymbols(QAbstractSpinBox::NoButtons);, depending on widget attribute <ShowButtons> (default true), so custom and legacy skins are not affected

This would make the decks grow so we also need to increase e.g. LateNight's minimum size.

Related: #11969

[ronso0]

Fixed by #12745 isn't it?

Feel free to reopen in case I missed some aspect.