optix: Fix coopvec emission

[mkeshavaNV]

While working on PR #7286 it was noticed that the emission of Coopvec has some issues. Here's the problem. Generate cuda output for the tests/cuda/optix-coopvec.slang test and you will see this:

#line 29
    OptixCoopVec<float, 4> _S8;

#line 29
    optixCoopVecTanh((_S6));

and then:

#line 29
    OptixCoopVec<float, 4> _S9 = _S8;

But it should be: OptixCoopVec<float, 4> _S8 = optixCoopVecTanh((_S6));

What I observe is that inside void CLikeSourceEmitter::emitInstResultDecl(IRInst* inst), I see that
for auto type = inst->getDataType();, type is returned as kIROp_VoidType. So this function terminates earlier because of this check:

if (as<IRVoidType>(type))
    return;

When creating the inst for tanh, I see:

 	slang.dll!Slang::IRBuilder::_createInst(unsigned __int64 minSizeInBytes, Slang::IRType * type, Slang::IROp op, __int64 fixedArgCount, Slang::IRInst * const * fixedArgs, __int64 varArgListCount, const __int64 * listArgCounts, Slang::IRInst * const * const * listArgs) Line 1866	C++
 	slang.dll!Slang::createInstImpl<Slang::IRCall>(Slang::IRBuilder * builder, Slang::IROp op, Slang::IRType * type, __int64 fixedArgCount, Slang::IRInst * const * fixedArgs, __int64 varArgListCount, const __int64 * listArgCounts, Slang::IRInst * const * const * listArgs) Line 1931	C++
 	slang.dll!Slang::createInstImpl<Slang::IRCall>(Slang::IRBuilder * builder, Slang::IROp op, Slang::IRType * type, __int64 fixedArgCount, Slang::IRInst * const * fixedArgs, __int64 varArgCount, Slang::IRInst * const * varArgs) Line 1952	C++
 	slang.dll!Slang::createInstWithTrailingArgs<Slang::IRCall>(Slang::IRBuilder * builder, Slang::IROp op, Slang::IRType * type, __int64 fixedArgCount, Slang::IRInst * const * fixedArgs, __int64 varArgCount, Slang::IRInst * const * varArgs) Line 2028	C++
 	slang.dll!Slang::IRBuilder::emitCallInst(Slang::IRType * type, Slang::IRInst * pFunc, unsigned __int64 argCount, Slang::IRInst * const * args) Line 3897	C++
 	slang.dll!Slang::IRBuilder::emitCallInst(Slang::IRType * type, Slang::IRInst * func, const Slang::List<Slang::IRInst *,Slang::StandardAllocator> & args) Line 4149	C++
>	slang.dll!Slang::makeFuncReturnViaOutParam(Slang::IRBuilder & builder, Slang::IRFunc * func) Line 75	C++
 	slang.dll!Slang::legalizeArrayReturnType(Slang::IRModule * module) Line 94	C++
 	slang.dll!Slang::linkAndOptimizeIR(Slang::CodeGenContext * codeGenContext, const Slang::LinkingAndOptimizationOptions & options, Slang::LinkedIR & outLinkedIR) Line 1695	C++
 	slang.dll!Slang::CodeGenContext::emitEntryPointsSourceFromIR(Slang::ComPtr<Slang::IArtifact> & outArtifact) Line 1995	C++
 	slang.dll!Slang::CodeGenContext::emitEntryPointsSource(Slang::ComPtr<Slang::IArtifact> & outArtifact) Line 794	C++
 	slang.dll!Slang::CodeGenContext::emitEntryPoints(Slang::ComPtr<Slang::IArtifact> & outArtifact) Line 1993	C++
 	slang.dll!Slang::TargetProgram::_createWholeProgramResult(Slang::DiagnosticSink * sink, Slang::EndToEndCompileRequest * endToEndReq) Line 2134	C++
 	slang.dll!Slang::EndToEndCompileRequest::generateOutput(Slang::TargetProgram * targetProgram) Line 2217	C++
 	slang.dll!Slang::EndToEndCompileRequest::generateOutput(Slang::ComponentType * program) Line 2586	C++
 	slang.dll!Slang::EndToEndCompileRequest::generateOutput() Line 2598	C++
 	slang.dll!Slang::EndToEndCompileRequest::executeActionsInner() Line 3940	C++
 	slang.dll!Slang::EndToEndCompileRequest::executeActions() Line 3949	C++
 	slang.dll!Slang::EndToEndCompileRequest::compile() Line 7510	C++
 	slang.dll!spCompile(slang::ICompileRequest * request) Line 720	C++
 	slangc.exe!_compile(slang::ICompileRequest * compileRequest, int argc, const char * const * argv) Line 54	C++
 	slangc.exe!innerMain(Slang::StdWriters * stdWriters, slang::IGlobalSession * sharedSession, int argc, const char * const * argv) Line 119	C++
 	slangc.exe!slangc_main(int argc, char * * argv) Line 129	C++
 	slangc.exe!wmain(int argc, wchar_t * * argv) Line 154	C++

In this callstack, we do makeFuncReturnViaOutParam(), so this ends up setting the type of tanh inst as void. Since this is void, inside void CLikeSourceEmitter::emitInstResultDecl(IRInst* inst)(), do an early return.

Steps to reproduce:

1. Generate the target cuda code like so:
   ./build/Debug/bin/slangc.exe .\tests\cuda\optix-coopvec.slang -target cuda -o out.cu -Xnvrtc -I"C:/ProgramData/NVIDIA Corporation/OptiX SDK 9.0.0/include" -I"C:/Program Files/NVIDIA GPU Computing Toolkit/CUDA/v12.8/include" -capability optix_coopvec

2. Observe that the generated code is as described in the issue here.

[mkeshavaNV]

The coopvec intrinsics emitted won't really compile correctly without this issue fixed correctly. However this work is currently not prioritized. Will be taking this up at a later point.