[clang-tidy][NFC] Reduce map lookups in IncludeSorter

Part of D117460, reduce multiple lookups on map
in IncludeSorter::addInclude method to one.

Author: PiotrZSL

clang-tools-extra/clang-tidy/utils/IncludeSorter.cpp

@@ -134,12 +134,13 @@ void IncludeSorter::addInclude(StringRef FileName, bool IsAngled,
   int Offset = findNextLine(SourceMgr->getCharacterData(EndLocation));
 
   // Record the relevant location information for this inclusion directive.
-  IncludeLocations[FileName].push_back(
+  auto &IncludeLocation = IncludeLocations[FileName];
+  IncludeLocation.push_back(
       SourceRange(HashLocation, EndLocation.getLocWithOffset(Offset)));
-  SourceLocations.push_back(IncludeLocations[FileName].back());
+  SourceLocations.push_back(IncludeLocation.back());
 
   // Stop if this inclusion is a duplicate.
-  if (IncludeLocations[FileName].size() > 1)
+  if (IncludeLocation.size() > 1)
     return;
 
   // Add the included file's name to the appropriate bucket.