Add an option to shrink window "hitboxes" for follow mouse

[vaxerski]

Discussion link

https://github.com/hyprwm/Hyprland/discussions/9884

Description

Currently, we use the window's "ideal" box (aka the layout box, including gaps, etc) for tracing follows_mouse.

For some users, that might be undesirable, as the focus switch could be quite aggressive.

Add an option to shrink those boxes by a set amount of layout pixels.

[ghost]

if we shrink the box wouldn't that also prevent clicks / interactions in the areas where the box doesn't stretch to?

[vaxerski]

yes, until it's focused, of course.