feat: added Focus Mode

[egonl]

When Focus Mode is enabled, Portion of Screen will automatically position itself over the currently focused window.

Focus Mode can be enabled in the Options dialog, which is available in the System Menu.

[dodjango]

following the focus ✅
resizing the focused window ✅
multi monitor, different scaling ❌
ignoring very small window size ✅

[dodjango]

⚠️ right click to open the options does not work. If you like, see this commit: dodjango@6cccc17

[egonl]

Right click isn't needed anymore, as there's now an Options menu:

[dodjango]

The PR description still says right click, therefore I mentioned it.

[egonl]

Updated description. I'm struggling with the scaling issue atm.

[Bzly]

Some thoughts on how this is working so far:

• I actually preferred the 'snappier' behaviour prior to #b466034
• Perhaps a special exception for the Alt-Tab and Win-Tab windows switchers, for privacy (these are shared along with general desktop when active) - could share a 1x1 black rectangle (or 0x0 if possible?), or some kind of privacy placeholder, or blur/pixelate instead.
• When the window border extends behind the task bar, the task bar is shown. It would be good if there was a check for window pos extending below taskbar height, and if so only drawing to there instead of screen edge.
• Can AUTO_REMOVE_CAPTION trigger based on whether PortionOfScreen is focused or not, rather than a timer?

It is working though, and I'm already looking forward to how much less frustrating meetings will be. Thanks!