Minor optimization and code cleanup in query_methods.

- Use symbols rather than strings where possible to avoid extra object construction
- Use destructive methods where possible to avoid extra object construction
- Use array union rather than concat followed by uniq
- Use shorthand block syntax where possible
- Use consistent multiline block styles, method names, method parenteses style, and spacing
Merge pull request #11693 from egilburg/minor_relation_refactor

Minor optimization and code cleanup in query_methods.rb