[clang] [llvm] [clang][hlsl] Add tan intrinsic part 1 (PR #90276)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

I'm worried if we add a whole new series of math intrinsics without adding the corresponding constrained intrinsics, it's going to be confusing for anyone trying to understand how math intrinsics work.  Why does tan exist, but not constrained tan?

`tan` is defined basically the same way as `sin` in Builtins.td; the only difference is that instead of `def SinF16F128 : Builtin, F16F128MathTemplate`, there's just `def TanF128 : Builtin {` (so no f16 support).

https://github.com/llvm/llvm-project/pull/90276