Fixes: mockito#2796

Add an optional method to `VarargMatcher`, which implementations
can choose to override to return the type of object the matcher is matching.

This is used by `MatcherApplicationStrategy` to determine if the type of matcher used to match a vararg parameter is of a type compatible with the vararg parameter.

Where a vararg compatible matcher is found, the matcher is used to match the _raw_ parameters.

...add the `type()` method to the `ArgumentMatcher` interface, rather than the `VarargMatcher` interface.

This would allow the, IMHO _broken_, `VarargMatcher` interface to be removed in a later major release.

fixes: mockito#1222