Testing: Add type annotations to common/logging

[rdimaio]

Part of #6588

On the ECS_FIELDS and LOG_RECORDS change, here's an execution of that code to show that the final BUILTIN_FIELDS is the same as before:

>>> from typing import TYPE_CHECKING, Any, Literal, Optional, Union, get_args
>>> ECS_FIELDS = Literal[
...     '@timestamp',
...     'message',
...     'log.level',
...     'log.origin.function',
...     'log.origin.file.line',
...     'log.origin.file.name',
...     'log.logger',
...     'process.pid',
...     'process.name',
...     'process.thread.id',
...     'process.thread.name'
... ]
>>>
>>> LOG_RECORDS = Literal[
...     'asctime',
...     'message',
...     'levelname',
...     'funcName',
...     'lineno',
...     'filename',
...     'name',
...     'process',
...     'processName',
...     'thread',
...     'threadName'
... ]
>>>
>>> BUILTIN_FIELDS = tuple((x, y) for x,y in zip(get_args(ECS_FIELDS), get_args(LOG_RECORDS)))
>>> BUILTIN_FIELDS
(('@timestamp', 'asctime'), ('message', 'message'), ('log.level', 'levelname'), ('log.origin.function', 'funcName'), ('log.origin.file.line', 'lineno'), ('log.origin.file.name', 'filename'), ('log.logger', 'name'), ('process.pid', 'process'), ('process.name', 'processName'), ('process.thread.id', 'thread'), ('process.thread.name', 'threadName'))