(NFC) Rename fiterable fields param in _civicrm_api3_basic_array_get …

[seamuslee001]

…to be more explicit about what it is for

Overview

This just renames a variable to be more explicit about what it accomplishes. This was found to be problematic through the work on the Extension API

ping @totten @eileenmcnaughton this should be very straight forward and should help in the future

[totten]

(CiviCRM Review Template WORD-1.0)

• (r-jira) Waive: Very small change. No benefit to extra process.
• (r-test) Undecided: Tests haven't finished running yet
• (r-code) Pass: Seems like an improvement in readability. Hopefully prevents misunderstandings.
• (r-doc) Pass
• (r-maint) Pass
• (r-run) Pass: There's really no UI/use-case. This is a utility function, and it has pretty good direct+indirect test-coverage.
• (r-user) Pass
• (r-tech) Pass: Renames a local variable, which should only impact code within one function. Examined the function to confirm that it was renamed consistently.

[seamuslee001]

This has passed tests now @eileenmcnaughton @totten