[clang] [HLSL][Docs] Update function calls docs (PR #106860)

[Sarah Spall via cfe-commits]

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@@ -248,13 +248,14 @@ which is a term made up for HLSL. A cx-value is a temporary value which may be
 the result of a cast, and stores its value back to an lvalue when the value
 expires.
 
-To represent this concept in Clang we introduce a new ``HLSLOutParamExpr``. An
-``HLSLOutParamExpr`` has two forms, one with a single sub-expression and one
-with two sub-expressions.
+To represent this concept in Clang we introduce a new ``HLSLOutArgExpr``. An
+``HLSLOutArgExpr`` has three sub-expressions:
 
-The single sub-expression form is used when the argument expression and the
-function parameter are the same type, so no cast is required. As in this
-example:
+* An OpaqueValueExpr of the argument lvalue expression.
+* An OpaqueValueExpr of the copy-initialized parameter temporary.
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spall wrote:

This is not always copy-initialized.  It is clarified later in the docs, so maybe its not worth mentioning here, but thought I'd point it out.

https://github.com/llvm/llvm-project/pull/106860