[clangd] Simplify code with *Map::operator[] (NFC) (#111939)

Author: kazutakahirata

clang-tools-extra/clangd/Headers.cpp

@@ -75,8 +75,8 @@ class IncludeStructure::RecordHeaders : public PPCallbacks {
               IDs.push_back(HID);
           }
       }
-      Out->MainFileIncludesBySpelling.try_emplace(Inc.Written)
-          .first->second.push_back(Out->MainFileIncludes.size() - 1);
+      Out->MainFileIncludesBySpelling[Inc.Written].push_back(
+          Out->MainFileIncludes.size() - 1);
     }
 
     // Record include graph (not just for main-file includes)

clang-tools-extra/clangd/XRefs.cpp

@@ -2282,8 +2282,7 @@ incomingCalls(const CallHierarchyItem &Item, const SymbolIndex *Index) {
       elog("incomingCalls failed to convert location: {0}", Loc.takeError());
       return;
     }
-    auto It = CallsIn.try_emplace(R.Container, std::vector<Range>{}).first;
-    It->second.push_back(Loc->range);
+    CallsIn[R.Container].push_back(Loc->range);
 
     ContainerLookup.IDs.insert(R.Container);
   });