Use floating DIPs throughout the stack

[lhecker]

I sure hope I didn't break anything! While til::math was a good idea its convenience led us to use it in the only place where it absolutely must not be used: The UI code. So, this PR replaces all those til::points, etc., with floats. Now we use DIPs consistently throughout all layers of the UI code, except for the UIA area (that would've required too many changes).

Validation Steps Performed

Launch, looks good, no obvious defects, UIA positioning seems ok. ✅