[clangd] Cleanup FuzzyFindRequest serialization and dex benchmark

* Due to the LLVM's JSON library changes (?), FuzzyFindRequest serialization is
  no longer valid since arrays are serialized as llvm::json::Array already.
  Hence, current implementation creates a nested array.
* YAML format is no longer the default, mention this for the benchmark.
* FIXME is no longer relevant. I ran benchmarks that showed no improvement with
  priority_queue years ago.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D106432

clang-tools-extra/clangd/benchmarks/IndexBenchmark.cpp

@@ -106,7 +106,7 @@ BENCHMARK(DexBuild);
 int main(int argc, char *argv[]) {
   if (argc < 3) {
     llvm::errs() << "Usage: " << argv[0]
-                 << " global-symbol-index.yaml requests.json "
+                 << " global-symbol-index.dex requests.json "
                     "BENCHMARK_OPTIONS...\n";
     return -1;
   }

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

@@ -49,12 +49,12 @@ bool fromJSON(const llvm::json::Value &Parameters, FuzzyFindRequest &Request,
 llvm::json::Value toJSON(const FuzzyFindRequest &Request) {
   return llvm::json::Object{
       {"Query", Request.Query},
-      {"Scopes", llvm::json::Array{Request.Scopes}},
+      {"Scopes", Request.Scopes},
       {"AnyScope", Request.AnyScope},
       {"Limit", Request.Limit},
       {"RestrictForCodeCompletion", Request.RestrictForCodeCompletion},
-      {"ProximityPaths", llvm::json::Array{Request.ProximityPaths}},
-      {"PreferredTypes", llvm::json::Array{Request.PreferredTypes}},
+      {"ProximityPaths", Request.ProximityPaths},
+      {"PreferredTypes", Request.PreferredTypes},
   };
 }
 

clang-tools-extra/clangd/index/dex/Iterator.cpp

@@ -207,7 +207,6 @@ private:
     return OS;
   }
 
-  // FIXME(kbobyrev): Would storing Children in min-heap be faster?
   std::vector<std::unique_ptr<Iterator>> Children;
   friend Corpus; // For optimizations.
 };