[HLSL] Handle init list with OpaqueValueExprs in CGExprScalar (#138541)
When an HLSL Init list is producing a Scalar, handle OpaqueValueExprs in
the Init List with 'emitInitListOpaqueValues'
Copied from 'AggExprEmitter::VisitCXXParenListOrInitListExpr'
Closes #136408
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Co-authored-by: Chris B <beanz@abolishcrlf.org>