fix: typing.Annotated should be special-cased like typing.Literal

[Daverball]

This is a partial fix for #192

This is probably not a huge change, since we skipped unexpected nodes within annotations already, so it would mostly get rid of some false positives where a string within Annotated happened to match one of the imported symbols and thus being treated as a forward reference incorrectly.

I still need to think about a solution for string annotations and whether or not we should visit the nodes we're currently skipping, maybe we should pass self into AnnotationVisitor so we can call the generic_visit of the outer visitor?

[Daverball]

I ended up switching to actually parsing string annotations with ast.parse rather than trying to keep getting away with a regex.

It's still not perfect, since starred expressions are only allowed within a subscript and there may come a time where further context specific syntax restrictions may complicate this even further. But for now I think this should be good enough.

[sondrelg]

Looks good to me @Daverball!