Minor refactoring of the API, to put optional arguments last. Also
changed internal structures to reflect that order, for consistency.
Also reduced size of Item from 88 to 72 bytes, by packing fields better.
Bug: webrtc:5696
Change-Id: I1b9d50831a8e9a358224682d06a782a3269b8416
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/264123
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37403}
b5754b00a6