Improve GraphQL pagination specs

What does this MR do?

This MR changes some of our shared examples that test GraphQL pagination.

They are aimed at simplifying the code and reducing the amount of string concatenation we are doing in order to build up queries.

One of the consequences of this is that we now need to pass arguments at the appropriate type. For enums this means Ruby symbols, so a number of spec files are updated to use symbols for :sort_param.

The SortEnum has an important update which is to align the values of the deprecated members and their replacements. Prior to this, the old values were all strings and the new ones all symbols. This fix exposed some subtle bugs which involved the new values being ignored as sort-orders in a few cases.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team