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

[Giulio Eulisse via cfe-commits]

================
@@ -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 {
----------------
ktf wrote:

```suggestion
  /// @return true in case the element at index @a Index belongs to a page which
  /// was already materialised.
  [[nodiscard]] bool isMaterialized(size_t Index) const {
```

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