To make sure inner gaps don't generate unequally sized windows always
apply a total of one inner gap to all children. Doing just this would
result in half-gaps around the workspace border so compensate for that
by adding gaps to the workspace.

Fixes swaywm#4296

Large inner gaps can lead to broken rendering with width/height going
negative. Limit the gaps so that they never make the windows smaller
than a minimum sensible size (the same used for the resize command).

Fixes swaywm#4294

Just like with inner gaps, outer gaps must be capped so that the
workspace doesn't run out of space. Since here we have different gaps in
all four directions clamp them in a way that at least maintains the
relative sizing of the gaps vertically and horizontally.

Fixes swaywm#4300

Since outer gaps can be negative we need to robustly prevent the
resulting gaps from ending up negative. The previous code only did this
on workspace creation but the gaps can change after that.

Fixes swaywm#4304