<rdar://problem/15449837>
<rdar://problem/15449837>

Change the NSSet data formatter to not use the expression parser to produce synthetic children
In small-scale experimentation with lldb-perf, this improves our performance by around 25%



git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@195294 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb