[clangd] Don't repeat class template args when printing constructor definitions

This fixes part of clangd/clangd#76

Author: sam-mccall

clang-tools-extra/clangd/XRefs.cpp

@@ -456,6 +456,7 @@ static std::string printDefinition(const Decl *D) {
   PrintingPolicy Policy =
       printingPolicyForDecls(D->getASTContext().getPrintingPolicy());
   Policy.IncludeTagDefinition = false;
+  Policy.SuppressTemplateArgsInCXXConstructors = true;
   D->print(OS, Policy);
   OS.flush();
   return Definition;

clang-tools-extra/clangd/unittests/XRefsTests.cpp

@@ -920,7 +920,7 @@ void foo())cpp";
          HI.Kind = SymbolKind::Constructor;
          HI.Type = "void ()";          // FIXME: Should be None
          HI.ReturnType = "void";       // FIXME: Should be None or X<T*>
-         HI.Definition = "X<type - parameter - 0 - 0 *>()"; // FIXME: --> X()
+         HI.Definition = "X()";
          HI.Parameters.emplace();
        }},