This will use the actual structure name or the override
from the trait as needed. Return value support
is also enabled in the code generation but not in
aws.zig. The current fuzzy checks should get most
of the way there though
Instead we will rely here on the implicit struct provided by the file
itself. This means that when the service_manifest.zig import is
assigned, we don't end up with a construct like "manifest.sts.sts" to
get to the sts service. This simplifies greatly the way that
servicemodel.zig needs to behave.
One down side, however, is that the structure does not seem
accessible with the current zig language, making metaInfo unable
to access itself as it did before. Or maybe it can, I just can't find
it. So, this change also adds a new "service_metadata" public constant
with the same declarations being published at the file level, and
that is the new return from the metaInfo function. Our aws.zig
only really needs the action and that metadata, so we're ok with that
even if there is some duplication (we could codegen pointers over, and
maybe should to save a little bit of space).
