In several cases we expected the target expression (e.g. e.X) of an indexer expression (i.e.IndexExp and IndexListExp) to be an *ast.Ident, which is not true for all cases. I wrote a test containing a bunch of the cases I could think of that would put a *ast. SelectorExpr as the target expression of the indexer expression. Most of the unhandled cases were around calling an exported generic function from a different package, e.g. package.Foo[int](). This must have slipped through the cracks when we were doing other generic stuff since it isn't too common in tests (ours and Go's) to have multiple packages.

I also fixed how exported functions are written to the package object. It was overwriting the package variable with the individual instances instead of setting the list of instances once.

This is related to #1013 and #1270