[clangd] Enable parsing of forwarding functions in the preamble by default

Fixes clangd/clangd#2324

Author: HighCommander4

clang-tools-extra/clangd/Compiler.h

@@ -40,7 +40,7 @@ class IgnoreDiagnostics : public DiagnosticConsumer {
 
 // Options to run clang e.g. when parsing AST.
 struct ParseOptions {
-  bool PreambleParseForwardingFunctions = false;
+  bool PreambleParseForwardingFunctions = true;
 
   bool ImportInsertions = false;
 };