[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

[via cfe-commits]

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@@ -2837,6 +2837,10 @@ bool QualType::hasNonTrivialToPrimitiveCopyCUnion(const RecordDecl *RD) {
   return RD->hasNonTrivialToPrimitiveCopyCUnion();
 }
 
+bool QualType::hasUninitializedExplicitInitFields(const RecordDecl *RD) {
----------------
higher-performance wrote:

The implementation is more complicated:
```
inline bool QualType::hasUninitializedExplicitInitFields() const {
  if (auto *RD = getTypePtr()->getBaseElementTypeUnsafe()->getAsRecordDecl())
    return hasUninitializedExplicitInitFields(RD);
  return false;
}
```
The other attributes right above this (like `hasNonTrivialToPrimitiveCopyCUnion`) are handled the same way, so I didn't imagine I should deviate from the pattern.

https://github.com/llvm/llvm-project/pull/102040