[clang] [NFC][Sema] Move `Sema::AssignmentAction` into its own scoped enum (PR #106453)

[Vlad Serebrennikov via cfe-commits]

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@@ -204,6 +204,24 @@ class SemaPPCallbacks;
 class TemplateDeductionInfo;
 } // namespace sema
 
+// AssignmentAction - This is used by all the assignment diagnostic functions
+// to represent what is actually causing the operation
+enum class AssignmentAction : unsigned {
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Endilll wrote:

```suggestion
enum class AssignmentAction {
```

https://github.com/llvm/llvm-project/pull/106453