Fix spelling of "resultset" which should be "result set"/"result_set"

Problem/Motivation

Per @xjm in #3323353: View combine filter operator "Is not equal to" use the same operator as "Is equal to":

I realize there's already the existing assertion with "resultset" cased as a single word, but let's not exacerbate the issue here. The local variable can be $result_set. :)

Tagging for a followup for "resultset" (ideally, we will rename the assertion method and fix all the copypasta of it as a single word, which can then be removed from the cspell dictionary.

Steps to reproduce

Search the code for 'resultset'

Proposed resolution

Fix the spelling
Remove from cspell dictionary (not sure it's in there actually)

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet