[clangd] Avoid including HeuristicResolver.h from ParsedAST.h

[nridge]

Motivation: ParsedAST.h is widely included (within clangd), and now that ParsedAST stores HeuristicResolver by unique_ptr, the header dependency is no longer necessary.

clang-tools-extra/clangd/ParsedAST.h

 
 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_PARSEDAST_H
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_PARSEDAST_H
 
 #include "CollectMacros.h"
 #include "Compiler.h"
 #include "Diagnostics.h"
 #include "Headers.h"
-#include "HeuristicResolver.h"
 #include "Preamble.h"
 #include "index/CanonicalIncludes.h"
 #include "support/Path.h"
 #include "clang/Frontend/FrontendAction.h"
 #include "clang/Frontend/PrecompiledPreamble.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "clang/Tooling/Syntax/Tokens.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringRef.h"
 #include <memory>
 #include <string>
 #include <vector>
 
 namespace clang {
 namespace clangd {
+class HeuristicResolver;
 class SymbolIndex;
 
 /// Stores and provides access to parsed AST.
 class ParsedAST {
 public:
   /// Attempts to run Clang and store the parsed AST.
   /// If \p Preamble is non-null it is reused during parsing.
   /// This function does not check if preamble is valid to reuse.

clang-tools-extra/clangd/ParsedAST.cpp

 #include "../clang-tidy/ClangTidyDiagnosticConsumer.h"
 #include "../clang-tidy/ClangTidyModuleRegistry.h"
 #include "AST.h"
 #include "Compiler.h"
 #include "Config.h"
 #include "Diagnostics.h"
 #include "FeatureModule.h"
 #include "Headers.h"
+#include "HeuristicResolver.h"
 #include "IncludeFixer.h"
 #include "Preamble.h"
 #include "SourceCode.h"
 #include "TidyProvider.h"
 #include "index/CanonicalIncludes.h"
 #include "index/Index.h"
 #include "support/Logger.h"
 #include "support/Trace.h"