Support for Generics

[gurleensethi]

Requested feature
Ability to create mocks when interfaces have generics used inside them.

Why the feature is needed
When I try to generate mocks I get this error:

2022/04/15 18:38:12 Loading input failed: service/my_service.go:7:11: failed parsing returns: don't know how to parse type *ast.IndexExpr

Would appreciate this feature being supported, for now it makes the combination go1.8 and gomock unusable.

[sodul]

I think this is a duplicate of #621

[codyoss]

Closing as dupe as mentioned above.