The current event-based approach is very difficult to get right, and it
depends on no events ever being missed. This changes the keyboard/mouse
handling code to a polling-based approach.
Other fixes:
- an issue where modifier keys were not able to be successfully bound
(like Left Shift to `X`)
- improves cursor hiding (except when you use the start menu, this seems
like an SDL issue, see comment)
- Better discarding of kb/mouse inputs when imgui intercepts input
- properly swap bindings when an already set key is assigned, even if it
crosses the distinction of an analog vs normal button
Fixes#2800
This moves the blerc math from mips2c to the Merc2 renderer, and uses
floats instead.
We could potentially do this on the GPU, which would be even faster, but
this isn't that slow in the first place.
Tyler Wilding