[🍒][llvm][cas] Add validate-if-needed to recover from invalid data#10602

mikeash merged 8 commits intoswiftlang:swift/release/6.2swiftlang/llvm-project:swift/release/6.2from

benlangmuir:eng/blangmuir/validate-if-needed-swift-123542312-release/6.2benlangmuir/llvm-project:eng/blangmuir/validate-if-needed-swift-123542312-release/6.2Copy head branch name to clipboard