"Universal" workspace panning

[yohannd1]

This PR adds the ability to pan through the workspace without having to click on the background. At the moment, the trigger I have used for this is the key combo Ctrl+Alt, which might not be ideal, but it was the most unique modifier combination I could think of.

vid.mp4

• 0:00 to 0:09 is the intended behavior.
• 0:12 shows a bug that appeared upon implementing this. Normal drag (no modifiers, just drag the background) works fine, but what I think is the first move mouse event is being handled in correctly, always resulting in a diagonal shift down-left.
• 0:16 is a "friendly" bug that does nothing, but is still confusing so I will try to fix it - you can begin the pan in any state, including when a window is maximized. I didn't show in the video but you can also begin it from the sidebar and the top bar.

Feedback is very welcome! I want to see if other people would have their workflow improved by being able to do this. I believe mine will.

Progress:

• Initial implementation
• Change keybinding: Ctrl+Alt -> Alt+S
• Fix offset bug (at 0:12 in the video)
• Add checks to prevent dragging in odd situations (at 0:16 in the video)
• Indicate more clearly when this action is happening (maybe show an indicator somewhere saying "pan-anywhere activated")
• Fix bug : panning without the keybinding, finishing and then trying to drag a widget is causing weird issues. Usually it tries to resize the widget.

[szeli1]

My concern with this PR is that it looks like to me that other "ctrl + alt" mouse shortcuts may not work because of the event filter. I did not test this PR.
Here is some code that may be effected:
AutomationEditor:

}
else if( we->modifiers() & Qt::ControlModifier && we->modifiers() & Qt::AltModifier )
{

ClipView:

bool ClipView::unquantizedModHeld( QMouseEvent * me )
{
	return me->modifiers() & Qt::ControlModifier || me->modifiers() & Qt::AltModifier;
}

PianoRoll:

void PianoRoll::dragNotes(int x, int y, bool alt, bool shift, bool ctrl)

[szeli1]

Suggested change

#include <QDebug> // TODO: remove

[yohannd1]

Will remove this right before I remove the draft state. I'm using it for debugging some things :)

[yohannd1]

Changed the keybinding to Alt+S, which (as discussed on discord) is not perfect. I'm hoping to find a better keybinding in the future but for now I'm leaving this one, which I believe doesn't have any conflicts.

Also a note to self: adding the keybinding handling on the event filter is sadly necessary, as when it is pressed I have to prevent it from being forwarded to other elements. I tried implementing it with key{Press,Release}Event and it was a mess.

[szeli1]

Also a note to self: adding the keybinding handling on the event filter is sadly necessary, as when it is pressed I have to prevent it from being forwarded to other elements. I tried implementing it with key{Press,Release}Event and it was a mess.

If I remember correctly, there are other options like implementing it in MainWindow::KeyPressEvent, or by using QAction with a shortcut in MainWindow, but event filter may be the best option.