[llvm] [clang][modules] Move `SLocEntry` search into `ASTReader` (PR #66966)

[Ben Langmuir via llvm-commits]

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@@ -1444,6 +1444,77 @@ llvm::Error ASTReader::ReadSourceManagerBlock(ModuleFile &F) {
   }
 }
 
+std::optional<SourceLocation::UIntTy>
+ASTReader::readSLocOffset(ModuleFile *F, unsigned Index) {
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benlangmuir wrote:

Does every path that returns `std::nullopt` report an error? If so I would recommend returning `Expected<...>` instead of `optional` and then report the error in the caller.

https://github.com/llvm/llvm-project/pull/66966