Support isinstance checks through ABCMeta for checkers and reporters

[brycepg]

Currently the PyLinter categorizes checkers through the __implements__ class attribute. This is not very standard, and is one more barrier for others to write plugins.

I propose

• Changing the interfaces to have a ABCMeta metaclass
• Change PyLinter to do isinstance checks to categorize checkers/reporters in addition to keeping the old __implements__ checks

[PCManticore]

This sounds good but note that we'd need to support the old style until we move the plugins to the new format.

[brycepg]

Agreed

[DanielNoord]

I'm going to take this on as a next step towards 3.0. I have been experimenting with this and it seems like this will be fairly easy to implement. The biggest difficulty comes from deprecating this in a clear way and giving plugins enough time to adapt.

It should be much less of a hassle (for us at least) than the argparse migration but will be crucial to put in 3.0.

As a first step I have been working on DanielNoord#129 which supports this for the first two interfaces.

[DanielNoord]

Note that the system we currently use seems to be based on a rejected PEP from 2001, see: https://peps.python.org/pep-0245/