[clang] [analyzer][NFC] Document and centralize the CallEvent argument/parameter index mapping (PR #221252)

[Donát Nagy via cfe-commits]

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@@ -420,6 +420,9 @@ class CallEvent {
   /// Returns memory location for a parameter variable within the callee stack
   /// frame. The behavior is undefined if the block count is different from the
   /// one that is there when call happens. May fail; returns null on failure.
+  ///
+  /// \param Index refers to the index of the declared parameter of the callee.
+  /// See getDeclaredParameterIndex().
   const ParamVarRegion *getParameterLocation(unsigned Index,
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NagyDonat wrote:

Consider renaming the parameter `Index` to `DeclParamIdx` (as you do in some other locations). The parameter name is e.g. displayed by some IDEs, so it is helpful to also encode this information in it.

https://github.com/llvm/llvm-project/pull/221252