[HLSL] implement `mad` intrinsic (#83826)

This change implements #83736
The dot product lowering needs a tertiary multipy add operation. DXIL
has three mad opcodes for `fmad`(46), `imad`(48), and `umad`(49). Dot
product in DXIL only uses `imad`\ `umad`, but for completeness and
because the hlsl `mad` intrinsic requires it `fmad` was also included.
Two new intrinsics were needed to be created to complete this change.
the `fmad` case already supported by llvm via `fmuladd` intrinsic.

- `hlsl_intrinsics.h` - exposed mad api call.
- `Builtins.td` - exposed a `mad` builtin.
- `Sema.h` - make `tertiary` calls check for float types optional. 
- `CGBuiltin.cpp` - pick the intrinsic for singed\unsigned & float also
reuse `int_fmuladd`.
- `SemaChecking.cpp` - type checks for `__builtin_hlsl_mad`. 
- `IntrinsicsDirectX.td` create the two new intrinsics for
`imad`\`umad`/
- `DXIL.td` - create the llvm intrinsic to  `DXIL` opcode mapping.

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Co-authored-by: Farzon Lotfi <farzon@farzon.com>