goose: use readable variable names

Names are inferred from types most of the time, but have a fallback for
a non-named type. Names are now also disambiguated from symbols in the
same scope.

Reviewed-by: Tuo Shan <shantuo@google.com>
Reviewed-by: Herbie Ong <herbie@google.com>

README.md

@@ -208,9 +208,6 @@ type MySQLConnectionString string
 
 ## Future Work
 
--   The names of imports and provider results in the generated code are not
-    actually as nice as shown above. I'd like to make them nicer in the
-    common cases while ensuring uniqueness.
 -   Support for map bindings.
 -   Support for multiple provider outputs.
 -   Currently, all dependency satisfaction is done using identity. I'd like to