[analyzer] Fix a bug in REGISTER_MAP_WITH_PROGRAMSTATE

The ImmutableMap should not be the key into the GDM map as there could
be several entries with the same map type. Thanks, Jordan.

This complicates the usage of the macro a bit. When we want to retrieve
the whole map, we need to use another name. Currently, I set it to be
Name ## Ty as in "type of the map we are storing in the ProgramState".

llvm-svn: 167000