[clangd] Improve printing of lambda names

[kadircet]

Summary

Clangd was printing lambdas as (anonymous class) before, we can
improve it by at least printing (lambda) instead.

[merge_guards_bot]

Unit tests: pass. 60959 tests passed, 0 failed and 726 were skipped.

clang-format: pass.

Build artifacts: diff.json, CMakeCache.txt, console-log.txt, test-results.xml

[ilya-biryukov]

LGTM

[kadircet]

Integrated into D71543

clang-tools-extra/clangd/AST.cpp

if (auto *UD = llvm::dyn_cast<UsingDirectiveDecl>(&ND)) {
     UD->getNominatedNamespaceAsWritten()->printName(Out);
     return Out.str();
   }
 
   if (isAnonymous(ND.getDeclName())) {
     // Come up with a presentation for an anonymous entity.
     if (isa<NamespaceDecl>(ND))
       return "(anonymous namespace)";
-    if (auto *Cls = llvm::dyn_cast<RecordDecl>(&ND))
+    if (auto *Cls = llvm::dyn_cast<RecordDecl>(&ND)) {
+      if (Cls->isLambda())
+        return "(lambda)";
       return ("(anonymous " + Cls->getKindName() + ")").str();
+    }
     if (isa<EnumDecl>(ND))
       return "(anonymous enum)";
     return "(anonymous)";
   }
 
   // Print nested name qualifier if it was written in the source code.
   if (auto *Qualifier = getQualifierLoc(ND).getNestedNameSpecifier())
     Qualifier->print(Out, PP);

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

void foo())cpp";
 
       // auto on lambda
       {R"cpp(
         void foo() {
           [[au^to]] lamb = []{};
         }
         )cpp",
        [](HoverInfo &HI) {
-         // FIXME: Special case lambdas.
-         HI.Name = "(anonymous class)";
+         HI.Name = "(lambda)";
          HI.Kind = index::SymbolKind::Class;
        }},
       // auto on template instantiation
       {R"cpp(
         template<typename T> class Foo{};
         void foo() {
           [[au^to]] x = Foo<int>();
         }