[clang-tools-extra] [clangd] Add background index format support to clangd-indexer (PR #175209)

[Jason Williams via cfe-commits]

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@@ -35,8 +35,9 @@ namespace clang {
 namespace clangd {
 
 enum class IndexFileFormat {
-  RIFF, // Versioned binary format, suitable for production use.
-  YAML, // Human-readable format, suitable for experiments and debugging.
+  RIFF,      // Versioned binary format, suitable for production use.
+  YAML,      // Human-readable format, suitable for experiments and debugging.
+  BACKGROUND // Background index format, suitable for language server use.
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jasonwilliams wrote:

I've renamed it to `SHARDED` instead, i don't think we need to worry about the combinations of --format and --index-type for now. `--format=sharded` should be enough for this

https://github.com/llvm/llvm-project/pull/175209