FEXCore/Utils: Implements a new atomic segmented bitmap allocator

[Sonicadvance1]

This is tailored towards our needs for our JIT and eventually replacing
the linear allocator. Allowing us to reallocate memory for code blocks
that have been invalidated, letting us keep a single code buffer around
for longer and using less memory overall.

In particular, high-invalidation games that ship anti-tamper tend to
emit millions of ~128-byte blocks in just a handful of minutes which
causes our current linear allocator to consume gigabytes very quickly.
This will allow us to more aggressively reuse the allocation space and
reduce the memory load in those situations.

There's some additional resize tuning that needs some work whence it is
in situ which doesn't need to be done now.

[lioncash]

Just two nits, but overall looks good