Start testing the construction of the Swift lookup tables in the Clang
importer for Objective-C entities. Fix some obvious issues, e.g.,
category and extension entries should be associated with the
corresponding class, and the categories/extensions shouldn't have
entries in the lookup table.
This places enumerators that will become either cases of a Swift enum
or options in a Swift option into the context of the C enum type for
the name lookup table.
This is needed for member lookup via the Swift lookup tables, although
the lookup part is not yet implemented. Note also that the results are
currently wrong for C enumerations mapped into Swift enums or option
sets. That will come shortly.
When we parse a bridging header, start building a mapping from Swift
names (both base names and full names) to the Clang declarations that
have those names in particular Clang contexts. For now, just provide
the ability to build the table (barely) and dump it out; we'll grow
it's contents in time.
