Make some cops aware of safe navigation operator

[koic]

Fixes #1191, #1192, #1193, #1194, #1196, #1197, #1201, and #1202.

This PR makes Rails/ActiveSupportAliases, Rails/FindBy, Rails/FindById, Rails/Inquiry, Rails/Pick Rails/PluckId, Rails/PluckInWhere, Rails/WhereEquals, Rails/WhereExists, and Rails/WhereNot cops aware of safe navigation operator.

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[ydakuka]

This is a violation for some cops.

ydakuka@yauhenid:~/Work/project$ bin/rails_docker rubocop app/models/user.rb 
Inspecting 1 file
W

Offenses:

app/models/user.rb:26:9: W: [Correctable] Lint/RedundantSafeNavigation: Redundant safe navigation detected.
    User&.where.not(name: 'Gabe')
        ^^^^^^^
app/models/user.rb:26:16: W: [Correctable] Lint/SafeNavigationChain: Do not chain ordinary method call after safe navigation operator.
    User&.where.not(name: 'Gabe')
               ^^^^^^^^^^^^^^^^^^

1 file inspected, 2 offenses detected, 2 offenses autocorrectable

I think I should be replaced with the following:

users = User.all
users&.where&.not(name: 'Gabe')

[koic]

Hm, this seems like an overreach for the role of this cop. The role is ensure that "manually constructed SQL in where can be replaced with where.not(...)" only.

[ydakuka]

irb(main):007:0> users = nil
=> nil
irb(main):008:0> users&.where.not(name: 'Gabe')
Traceback (most recent call last):
        1: from (irb):8
NoMethodError (undefined method `not' for nil:NilClass)

[koic]

Good catch. I've updated it.

[ydakuka]

irb(main):010:0> users = nil
=> nil
irb(main):011:0> users&.where(name: 'john').exists?
Traceback (most recent call last):
        1: from (irb):11
NoMethodError (undefined method `exists?' for nil:NilClass)