Inspect inline style for FactoryBot/AssociationStyle

[r7kamura]

Since there has been a long-standing desire to do so, I've made FactoryBot/AssociationStyle capable of handling inline associations.

• Resolves Redundant blocks for factory and association #81

Specifically, the need for inline association support has increased recently because autocorrection that generates inline association code has been newly added in the following change:

• Add autocorrect for FactoryBot/FactoryAssociationWithStrategy #166

Simply put, code like the following, which was not considered an offense until now, will now be regarded as an offense:
(In addition, it supports autocorrect except for complex situations.)

# bad
factory :post do
  user { association :user }
end

# good
factory :post do
  association :user
end

For this change, I decided not to support EnforcedStyle: inline. This is because I personally have no desire to recommend the inline style even in situations where it can be substituted with other styles. Logically, it is feasible, but I believe it should only be supported when a clear use case emerges in the future.

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• Added the new cop to config/default.yml.
• The cop is configured as Enabled: pending in config/default.yml.
• The cop documents examples of good and bad code.
• The tests assert both that bad code is reported and that good code is not reported.
• Set VersionAdded: "<<next>>" in default/config.yml.

If you have modified an existing cop's configuration options:

• Set VersionChanged: "<<next>>" in config/default.yml.

[r7kamura]

Other changes to the same cop are proceeding in parallel, and it's clear they will conflict, so I've put this change on hold in a draft state. Since this change is larger in scope, I believe it would be smoother to address the smaller, earlier changes first, and then handle this one.

• Fix a false negative for FactoryBot/AssociationStyle when using implicit associations in global traits #167
• Fix a false negative for FactoryBot/AssociationStyle when using keyword traits with explicit associations #168
• Fix a false positive for FactoryBot/AssociationStyle when strategy option is used #169