GlCollapsibleDropdown > Micro-optimizations and refactors
What does this MR do?
This addresses a few last-minute comments from !3285 (merged):
- 2d13b6ec micro-optimizes a helper that loops over a slot's nodes. Addresses !3285 (comment 1281391841).
- a4414e98 cleans up a story helper to make arguments easier to grasp. Addresses !3285 (comment 1281391854).
- 0d2b2382 adds a missing test-case. Addresses !3285 (comment 1281391857).