Update RSpec/SharedExamples to allow specifying a preferred method to use for defining and including shared examples and context

[dvandersluis]

Allows RSpec/SharedExamples to be configured with preferred methods for defining and including shared examples and context, so that consistency can be enforced.

Follows rubocop/rubocop#14033.

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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 is configured as Enabled: true in .rubocop.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.

[dvandersluis]

I'm unclear as to why, but simplecov doesn't think this branch is covered, even though it is (line 270 of the spec).

[dvandersluis]

Failing edge rubocop check is fixed in #2063.

[pirj]

Nice!

Glancing over, it feels this would better be a separate cop. Do you have a specific reason to modify the existing one?

Once concern that comes to mind is that new cops are pending by default. We're releasing major versions more often, and in less than a year this cop will be enabled for everyone.

[dvandersluis]

@pirj ha! I went back and forth on if it should enhance the existing cop or create a new one. I settled on updating because RSpec/SharedExamples seems like the right name for this and I wasn't sure what to name a new cop as. Do you have a suggestion?

[pirj]

I don't think we had a chance to adjust cop names to follow the cop naming guidelines, but I'd call those two RSpec/IncorrectSharedExampleAlias and RSpec/IncorrectSharedExampleHandleType. Now they look more like Java class names, though.

[dvandersluis]

How about for these changes RSpec/PreferredSharedExampleMethods?

[dvandersluis]

I'll open a new PR with the new cop.