Expose PatchSetParser utility class to be used from plugins

Plugins can offer similar SSH commands like `gerrit review` and should
be able to re-use this core facility to parse COMMIT | CHANGE,PATCHSET
arguments.

Change-Id: I076466d7ae413bd63e149b77ccba32a1f24ed7a6

gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/PatchSetParser.java

@@ -34,7 +34,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 @Singleton
-class PatchSetParser {
+public class PatchSetParser {
   private final Provider<ReviewDb> db;
   private final Provider<InternalChangeQuery> queryProvider;
   private final ChangeNotes.Factory notesFactory;