Python: all: Rename Bare* classes to Raw* and clarify low-level usage

[eavanvalkenburg]

Rename Bare* classes:

• Use Raw* when appropriate for low-level classes that should almost never be used directly
• Still use Base* for things that are actual base classes (meaning they are ABC or have abstract methods)

Make very clear that Raw* classes are very low-level classes that should almost never be used directly.

Parent issue: #3575