<rdar://problem/11338654> Fixing a bug where having a summary for a bitfield...

<rdar://problem/11338654> Fixing a bug where having a summary for a bitfield without a format specified would in certain cases crash LLDB - This has also led to refactoring the by-type accessors for the data formatter subsystem. These now belong in our internal layer, and are just invoked by the public API stratum

llvm-svn: 156429