Revert "[libc][NFC] Implement `FPBits` in terms of `FloatProperties` to reduce clutter" (#75304)

Reverts llvm/llvm-project#75196

GCC complains about change of meaning for `FPBits`
```
/home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian-fullbuild/libc-x86_64-debian-gcc-fullbuild-dbg/llvm-project/libc/src/__support/FPUtil/generic/FMod.h:188:9: error: declaration of ‘using FPBits = struct __llvm_libc_18_0_0_git::fputil::FPBits<T>’ changes meaning of ‘FPBits’ [-fpermissive]
  188 |   using FPBits = FPBits<T>;
      |         ^~~~~~
```

I'll reland with a different name.