[clang] Avoid need for SLocEntryLoaded BitVector (PR #67960)

[Jakub Kuderski via cfe-commits]

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@@ -103,6 +103,12 @@ template <typename T, size_t PageSize = 1024 / sizeof(T)> class PagedVector {
   /// Return the size of the vector.
   [[nodiscard]] size_t size() const { return Size; }
 
+  [[nodiscard]] bool isMaterialized(size_t Index) const {
+    assert(Index < Size);
+    assert(Index / PageSize < PageToDataPtrs.size());
+    return PageToDataPtrs[Index / PageSize] != nullptr;
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kuhar wrote:

```suggestion
    return PageToDataPtrs[Index / PageSize];
```

https://github.com/llvm/llvm-project/pull/67960