Rename FileList cache to DiffSummary

We want to store the number of inserted/deleted lines in this cache in
addition to the file list.

Change-Id: Iaa6414c5e99d1c5724c99ac677c2fd9522ef6b05

gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListCache.java

@@ -34,6 +34,6 @@ public interface PatchListCache {
   IntraLineDiff getIntraLineDiff(IntraLineDiffKey key,
       IntraLineDiffArgs args);
 
-  FileList getFileList(Change change, PatchSet patchSet)
+  DiffSummary getDiffSummary(Change change, PatchSet patchSet)
       throws PatchListNotAvailableException;
 }