[SYCL] Implement sycl_ext_oneapi_fp8 for CRI (#21568)

This PR adds FP8 types for CRI
[docs](https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/proposed/sycl_ext_oneapi_fp8.asciidoc).
It adds the first part which includes:

1. Initial implementation
2. Unit tests which check expected behavior and values
3. Unit tests which check the fact of builtin calls.
4. E2E tests of all 3 data types: fp8_e4m3, fp8_e5m2 and fp8_e8m0

---------

Co-authored-by: Copilot <copilot@github.com>

Author: dklochkov-emb

llvm/lib/SYCLPostLink/ModuleSplitter.cpp

@@ -93,7 +93,8 @@ bool isSpirvSyclBuiltin(StringRef FName) {
   // now skip the digits
   FName = FName.drop_while([](char C) { return std::isdigit(C); });
 
-  return FName.starts_with("__spirv_") || FName.starts_with("__sycl_");
+  return FName.starts_with("__spirv_") || FName.starts_with("__sycl_") ||
+         FName.starts_with("__builtin_spirv_");
 }
 
 // Return true if the function is a ESIMD builtin

llvm/test/tools/sycl-post-link/sycl-external-funcs/drop-known-builtins.ll

@@ -24,10 +24,19 @@ define dso_local spir_func void @_Z33__sXcl_getScalarSpecConstantValue() #0 {
   ret void
 }
 
+define dso_local spir_func void @_Z29__builtin_spirv_foo() #0 {
+  ret void
+}
+define dso_local spir_func void @_Z29__builtin_spXrv_foo() #0 {
+  ret void
+}
+
 attributes #0 = { "sycl-module-id"="a.cpp" }
 
 ; CHECK-NOT: define dso_local spir_func void @_Z28__spirv_GlobalInvocationId_xv()
 ; CHECK-NOT: define dso_local spir_func void @_Z33__sycl_getScalarSpecConstantValue()
+; CHECK-NOT: define dso_local spir_func void @_Z29__builtin_spirv_foo()
 
 ; CHECK-DAG: define dso_local spir_func void @_Z28__spXrv_GlobalInvocationId_xv()
 ; CHECK-DAG: define dso_local spir_func void @_Z33__sXcl_getScalarSpecConstantValue()
+; CHECK-DAG: define dso_local spir_func void @_Z29__builtin_spXrv_foo()