[libc][math][c++23] Implement BFloat16 higher math functions

This issue serves as the meta issue for all higher math functions for the BFloat16 type.
Please also see https://libc.llvm.org/headers/math/index.html.

- [x] `acosbf16`: https://github.com/llvm/llvm-project/pull/184633
- [ ] `acoshbf16`
- [ ] `acospibf16`
- [x] `asinbf16`: https://github.com/llvm/llvm-project/pull/184170
- [ ] `asinhbf16`
- [ ] `asinpibf16`
- [x] `atanbf16`: https://github.com/llvm/llvm-project/pull/184019
- [ ] `atan2bf16`
- [ ] `atan2pibf16`
- [ ] `atanhbf16`
- [ ] `atanpibf16`
- [x] `cbrtbf16`: https://github.com/llvm/llvm-project/pull/180327
- [ ] `compoundnbf16`
- [ ] `cosbf16`
- [ ] `coshbf16`
- [ ] `cospibf16`
- [ ] `erfbf16`
- [ ] `erfcbf16`
- [x] `expbf16`: https://github.com/llvm/llvm-project/pull/161919
- [ ] `exp10bf16`
- [ ] `exp10m1bf16`
- [ ] `exp2bf16`
- [ ] `exp2m1bf16`
- [ ] `expm1bf16`
- [x] `fmabf16`: https://github.com/llvm/llvm-project/pull/182836
- [x] `hypotbf16`https://github.com/llvm/llvm-project/pull/183460
- [ ] `lgammabf16`
- [x] `log_bf16`: https://github.com/llvm/llvm-project/pull/157811
- [ ] `log10bf16`: https://github.com/llvm/llvm-project/pull/177269
- [ ] `log10p1bf16`
- [ ] `log1pbf16`
- [ ] `log2bf16`: https://github.com/llvm/llvm-project/pull/177275
- [ ] `log2p1bf16`
- [ ] `logp1bf16`
- [ ] `powbf16`
- [ ] `pownbf16`
- [ ] `powrbf16`
- [ ] `rootnbf16`
- [ ] `rsqrtbf16`
- [ ] `sinbf16`
- [ ] `sincosbf16` (extension)
- [ ] `sinhbf16`
- [ ] `sinpibf16`
- [x] `sqrtbf16`: https://github.com/llvm/llvm-project/pull/156654
- [x] `tanbf16`: https://github.com/llvm/llvm-project/pull/185100
- [ ] `tanhbf16`
- [ ] `tanpibf16`
- [ ] `tgammabf16`