Rename LightningLoggerBase to Logger

[daniellepintz]

Proposed refactor

• Create a new file loggers/logger.py
• In that file, create a new Logger class by copying the code in LightningLoggerBase
• Make LightningLoggerBase subclass Logger, and create a dummy constructor to emit a deprecation warning like in this example:
  https://github.com/PyTorchLightning/pytorch-lightning/blob/d61371922bf89a2b810711e67eee47f224be60cc/pytorch_lightning/plugins/training_type/ddp.py#L18-L24

Motivation

We want all of our main class names to follow the same standard. Logger should match Callback, Strategy, Accelerator, etc. Also, we want our files names to conform to standard of accelerators/accelerator.py, strategies/strategy.py, etc.

Part of #11908

cc @justusschock @awaelchli @rohitgr7 @edward-io @Borda @ananthsub @kamil-kaczmarek @Raalsky @Blaizzy

[MohammedAlkhrashi]

Hi, if no one has been assigned yet, can I work on this issue?

[daniellepintz]

Yup, just assigned you!! Thanks!