[git] IDEA-118265 Fix showing Git Branches menu

The original fix (007dc0d) was incorrectly applied (a98e6c8d) because of
the patch context difference.

Move getCommonBranches to GitBranchUtil &
change retainAll() to intersection().
Now contents of GitBranchUtil and GitMultiRootBranchConfig
are identical in both master & release branches.
Merge remote-tracking branch 'origin/133' into 133