Change how microsurveys are structured. This ensures that screen readers
perceive a single logical collection, which contains all the radio
buttons and is labeled by the question, which is no longer defined by
subtitle but by tiles.label. This also changes how survey randomization
works. Instead of randomizing the entire set, we randomize specific
items. Any adjacent items with randomize will be randomized in-place. So
if there are 4 items with randomize, followed by 1 nonrandom item, the 4
will be randomized but the 5th will stay at the bottom. Finally, this
patch saves the randomized order so that it persists between back and
forward navigation on about:welcome. That should avoid some jank if we
show surveys in about:welcome.
Differential Revision: https://phabricator.services.mozilla.com/D202513
9c7d018917