[SPIRV] Add FloatControl2 capability (#144371)

Add handling for FPFastMathMode in SPIR-V shaders. This is a first pass
that
simply does a direct translation when the proper extension is available.
This will unblock work for HLSL. However, it is not a full solution.

The default math mode for spir-v is determined by the API. When
targeting Vulkan many of the fast math options are assumed. We should do
something particular when targeting Vulkan.

We will also need to handle the hlsl "precise" keyword correctly when
FPFastMathMode is not available.

Unblockes https://github.com/llvm/llvm-project/issues/140739, but we are
keeing it open to track the remaining issues mentioned above.

llvm/docs/SPIRVUsage.rst

@@ -217,6 +217,8 @@ list of supported SPIR-V extensions, sorted alphabetically by their extension na
      - Adds an instruction to compute the matrix product of an M x K matrix with a K x N matrix and then add an M x N matrix. 
    * - ``SPV_INTEL_int4``
      - Adds support for 4-bit integer type, and allow this type to be used in cooperative matrices.
+   * - ``SPV_KHR_float_controls2``
+     - Adds ability to specify the floating-point environment in shaders. It can be used on whole modules and individual instructions.
 
 To enable multiple extensions, list them separated by comma. For example, to enable support for atomic operations on floating-point numbers and arbitrary precision integers, use: