add loopmove equivalents for beatloop: `loopmove_size`, `loopmove_forward`, `loopmove_backward`

[ronso0]

Feature Description

Turns out that beatjump automatically doing loopmove when a loop is active causes some confusion, and also undesired side effects:

1. beatjump in active loops is not possible / tedious / dangerous
   -> you need to quickly disable the loop, beatjump, re-enable loop -> dangerous as we may cross the loop out marker and fall out of sync when re-enabling the loop
2. Beatjump moves cue loops #16149 beatjump moves saved loops
3. usually I want to move the loop just a tiny bit, or by 1/2/4 beats, but my beatjump size is usually 8/16/32 beats
   -> moving the loop requires to change the beat size spinbox

Controller mappings with Loop Move pads are not affected, they can use the existing loopmove_[beats]_foward controls

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I propose to add

• loopmove_size
• loopmove_forward -> using loopmove_size
• loopmove_backward -> using loopmove_size

I already opened #16099 which adds the Preferences option "Beatjump moves the active loop"

Regarding the skins:

1. add optional Loopmove controls, but skins are already pretty crammed.
2. keep the current spinbox / Fwd / Back button, but add 'Loop'|'Jump' radio buttons that would swap the sections, so either loopmove or beatjump controls are displayed
3. keep as is and make Shift + Fwd/Back do Loopmove when the auto-loopmove option is disabled
   = add ShiftLeftButton and ShiftRightButton connections to WPushButton, requires to extend the ButtonState enum

For now I'd do 3. Though only for 1-state buttons like the loopmove/beatjump buttons, because I'm afraid that WPushButton::mousePressEvent/mouseReleaseEvent will become unmanagably complex if we do this for multi-state buttons.

TODO

• make auto-loopmove optional make beatjump moving active loop optional #16099
• add loopmove_size + loopmove_forward+ loopmove_backward
• adjust skins

What do you think?