Added a new method .captor(U...) on the ArgumentCaptor class that has the same interface as Mockito.mock(U...) with the goal of removing the need for unchecked-warning suppression when users make use of generic types in argument captors.

This allows the following usage without raising compiler warnings:

ArgumentCaptor<List<Thingy>> thingyCaptor = ArgumentCaptor.captor();

...rather than the current solution, which is less elegant...

@SuppressWarnings({"unchecked", "rawtypes"})
ArgumentCaptor<List<Thingy>> thingyCaptor = (ArgumentCaptor<List<Thingy>>) ArgumentCaptor.forClass(List.class);

A side effect of wanting to write tests for this meant I needed to expose the class held within a captor, so an additional method named .getCaptorType() has also been added. I have added this as public as it feels like a useful thing to expose anyway, given the user will know what is held internally. However, if this is unacceptable then I am happy to demote it to package-private or remove it and replace it with something like assertThat(captor).hasPropertyOrFieldWithValue("clazz", expectedClass);, or anything else that is suggested.

Checklist

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