<rdar://problem/12978143>

Data formatters now cache themselves.
This commit provides a new formatter cache mechanism. Upon resolving a formatter (summary or synthetic), LLDB remembers the resolution for later faster retrieval.
Also moved the data formatters subsystem from the core to its own group and folder for easier management, and done some code reorganization.
The ObjC runtime v1 now returns a class name if asked for the dynamic type of an object. This is required for formatters caching to work with the v1 runtime.
Lastly, this commit disposes of the old hack where ValueObjects had to remember whether they were queried for formatters with their static or dynamic type.
Now the ValueObjectDynamicValue class works well enough that we can use its dynamic value setting for the same purpose.