Enable Rubocop cops that check access modifiers
## What does this MR do?
This MR enables Rubocop cops that detect methods that should be restricted but are the part of public API because of access modifiers used improperly.
This also fixes existing offenses.
## Why was this MR needed?
Some method in our codebase are public instead of being private because it is sometimes difficult to get it right without static analysis.
## What are the relevant issue numbers?
See #17478Closes#17372
See merge request !5014
