Generate a class that includes all the Activity's deep link params

Right now you have to extract deep link parameters from the Intent extras, which is still pretty error prone since there is no compile time validation. We could leverage our annotation processor here to generate a class that contains all the Activity's deep link parameters, say `FooActivity_DeepLink` where you'd retrieve all the information from methods in this activity.

Start by reading the annotation processor and the Activity deep-link handling that currently extracts parameters from Intent extras. Determine how an Activity's declared deep-link parameters can be represented in generated methods. Done means each Activity has a generated FooActivity_DeepLink class that exposes its parameters with compile-time validation.

Written by the indexing model from the issue text.