Use all monitor(s) geometry to determine hot corner positions (linuxmint#7726)

[codewithmichael]

Fixes #7726

Description:

Avoids hard-to-trigger "corner" points between monitors on dual/multi-monitor setups by moving hot corner positions to the outer edge.

Change Summary:

• Updated the HotCornerManager.updatePosition() to (optionally) accept multiple monitors for use in determining hot corner positions.
• Updated LayoutManager._updateBoxes() to pass all connected monitors instead of just primaryMonitor.

[mtwebster]

Hi, there a few things here:

• This would be a regression for people that might being using hot corners on shared edges of a multi-monitor setup.
• There's an option for only showing a workspace overview (expo) that only displays the primary monitor - using a hot corner to activate this could be confusing with this option activated.

It's probably a fairly common case also, since the issue goes away with adjacent panels on adjacent monitors - barriers are added by default (panel settings->allow pointer to pass thru edges of panels).

These barriers are probably the best solution for the original problem - if an 'inner' corner is active, place a barrier there to keep the pointer from overshooting.

Maybe in a later patch multi-monitor support could be added (adding corners to more than the primary monitor).

The pointer barriers are not terribly complicated - it's implemented in cinnamon's panel.js file if you're interested in taking a look - if you'd like update this pr (or open a new one later).

Thanks