Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)

Takes the logic from Jit64 and moves it into DivUtils, so it can be
reused by other backends as well.

This should prevent issues like the one fixed in the previous commit
from happening again.

This is a little trick I came up with that lets us restructure our float
classification code so we can exit earlier when the float is normal,
which is the case more often than not.

First we shift left by 1 to get rid of the sign bit, and then we count
the number of leading sign bits. If the result is less than 10 (for
doubles) or 7 (for floats), the float is normal. This is because, if the
float isn't normal, the exponent is either all zeroes or all ones.

This fixes a bunch of DEBUG_ASSERTs in the unit tests.