deprecate locale switching during runtime

[xDivisionByZerox]

Clear and concise description of the problem

I don't see a use case where you wouldn't be able to instantiate a new faker instance with your desired locale and instead need the utility to change an instance's locale during runtime.

Dropping this feature allows some easier separation of concern handling and thus leading to a cleaner architecture for the library.

Suggested solution

Deprecate (and later remove) the public accessibility of:

• faker.locale
• faker.locales
• faker.localeFallback
• faker.setLocal()

Alternative

No response

Additional context

There is a poll for dropping the feature of switching locales during runtime.

[Shinigami92]

This needs to be done together with e.g. #642, because with out that, it's nearly impossible to build own Faker instances.

[ST-DDT]

IMO its more like a precondition.

[ST-DDT]

Superseded by #1340