[clangd] Use xxh3_64bits for background index file digests

Many sources show that xxh3 is much better than xxh64. This particular
instance may or may not have noticeable difference, but this change
moves us toward removing xxHash64.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D155992

clang-tools-extra/clangd/SourceCode.cpp

@@ -559,7 +559,7 @@ TextEdit toTextEdit(const FixItHint &FixIt, const SourceManager &M,
 }
 
 FileDigest digest(llvm::StringRef Content) {
-  uint64_t Hash{llvm::xxHash64(Content)};
+  uint64_t Hash{llvm::xxh3_64bits(Content)};
   FileDigest Result;
   for (unsigned I = 0; I < Result.size(); ++I) {
     Result[I] = uint8_t(Hash);

clang-tools-extra/clangd/index/Background.cpp

@@ -155,7 +155,7 @@ static llvm::StringRef filenameWithoutExtension(llvm::StringRef Path) {
 
 BackgroundQueue::Task BackgroundIndex::indexFileTask(std::string Path) {
   std::string Tag = filenameWithoutExtension(Path).str();
-  uint64_t Key = llvm::xxHash64(Path);
+  uint64_t Key = llvm::xxh3_64bits(Path);
   BackgroundQueue::Task T([this, Path(std::move(Path))] {
     std::optional<WithContext> WithProvidedContext;
     if (ContextProvider)

clang-tools-extra/clangd/index/Serialization.cpp

@@ -457,7 +457,7 @@ readCompileCommand(Reader CmdReader, llvm::ArrayRef<llvm::StringRef> Strings) {
 // The current versioning scheme is simple - non-current versions are rejected.
 // If you make a breaking change, bump this version number to invalidate stored
 // data. Later we may want to support some backward compatibility.
-constexpr static uint32_t Version = 18;
+constexpr static uint32_t Version = 19;
 
 llvm::Expected<IndexFileIn> readRIFF(llvm::StringRef Data,
                                      SymbolOrigin Origin) {