[SPIR-V] Legalize the llvm.is.fpclass intrinsic

[Icohedron]

Description

LLVM Language Reference: llvm.is.fpclass

The lowering of llvm.is.fpclass depends on the compile-time constant operand i32 <test>.
Valid bits for <test> are defined in an enum named FPClassTest.
The following FPClassTest cases are of interest:

• FPClassTest::fcInf, FPClassTest::fcNan, FPClassTest::fcFinite, FPClassTest::fcNormal map directly to SPIR-V Ops

The lowering of llvm.is.fpclass to both SPIR-V and DirectX will simplify the codegen for HLSL intrinsics isinf, isnan, and isfinite

SPIRV Ops

• OpIsInf
• OpIsNan
• OpIsNormal
• OpIsFinite

Note: The SPIRV specification states that the results of these ops depends on the floating-point encoding used. However, there are currently no alternative floating-point encodings listed in the specification.

[Icohedron]

As mentioned in #87777 (comment), isnan and isinf will not use llvm.is.fpclass because they should not be removed by fast-math optimizations.
isfinite should be implemented with its own intrinsic as well, to be consistent with isnan and isinf.