AVRO-3694: [py] compatibility correlate messages with locations

[oshevtsov]

What is the purpose of the change

This pull request improves incompatibility check (in the python client) of two avro schemas by grouping together incompatibility type, explanation message, and schema location together in a single data structure, fixing AVRO-3694.

Verifying this change

This change is already covered by existing tests, such as /lang/py/avro/test/test_compatibility.py.

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)