[Fix #9621] Add consistent style to Lint/SymbolConversion to require all symbol keys in a hash to use the same convention

[dvandersluis]

The consistent style works the same as the previous default style (now called strict), in that symbol conversions should be explicit. However, in the case of a hash with a mix of symbol keys requiring quoting and not, this style now enforces that all keys are quoted for consistency.

Fixes #9621.

---

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.

[dvandersluis]

@rubocop/rubocop-core one thing that I'm not sure about is that Lint cops generally do not have configurable styles; Lint/InheritException is the only other one. However, this behaviour can't be enforced by a separate Style cop unless Lint/SymbolConversion is updated to ignore some cases if that cop is enabled, which is another can of worms. Maybe someone has an idea?

Separately, I am using the configuration from Style/StringLiterals to determine how to quote the keys. We don't currently have anything checking for consistency of quote style in quoted symbol literals.

[bbatsov]

@rubocop/rubocop-core one thing that I'm not sure about is that Lint cops generally do not have configurable styles; Lint/InheritException is the only other one. However, this behaviour can't be enforced by a separate Style cop unless Lint/SymbolConversion is updated to ignore some cases if that cop is enabled, which is another can of worms. Maybe someone has an idea?

Most Lint cops shouldn't have different supported styles, but I guess that's OK in the current situation. Alternatively this can also be some flag like "AllowConsistentSymbolsInHash" or something along those lines. I'm fine with the current approach as well.

Separately, I am using the configuration from Style/StringLiterals to determine how to quote the keys. We don't currently have anything checking for consistency of quote style in quoted symbol literals.

I think that's fine.

[bbatsov]

Might be a good idea to add the strict case for hashes as well, so it's clearer what this means for them.

[dvandersluis]

@bbatsov I added additional documentation, thanks!

[bbatsov]

Thanks!