[libc] [llvm] [libc][math][c23] Add fsqrtf16 C23 math functions. (PR #131153)

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lntue wrote:

Sorry what I meant was that, the square root function that take `float` input and return `float16` would be named `f16sqrtf`, which is already implemented.  And there will NOT be `fsqrtf16` function, because following the naming, it is supposed to take `float16` input, and return `float` output.  But `float` is wider than `float16`.

https://github.com/llvm/llvm-project/pull/131153