Allow ActiveRecord::QueryMethods#pluck to accept hash args with symbol & string values

[joshuay03]

Motivation / Background

Extends the feature added in #51565 to allow symbol and string hash values when plucking a single column for a specific table. When trying out this new feature I naturally thought this was already valid seeing as the API is common in other query methods (with differing functionality based on the method) e.g. includes(foo: :bar), order(foo: :desc).

Post.joins(:comments).pluck(:id, comments: :id)

Detail

Updates ActiveRecord::QueryMethods#arel_columns_from_hash which is used by #pluck to simply return the Arel attribute for the column by default if the hash value is a symbol or string, while maintaining #select specific aliasing functionality.

Additional information

While working on this I realised that #51565 introduced a bit of a non-obvious side effect where a query like:

Post.joins(:comments).pluck(:id, comments: { id: :foo })

would return the correct results, but also alias the column in the query ("comments"."id" AS foo).

Just thought it was worth mentioning in case this is classified as a 'bug'. If so, it might be worth separating out the #select specific logic from the rest (or #pluck from the rest), which would also simplify the conditional logic for the extension in this PR.

cc/ @fatkodima Keen for your thoughts on this feature and my last note.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Unrelated changes should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[joshuay03]

This is a bit hacky, see my note in the 'Additional information' section for a possible alternative.