[FORMS-2] Async loading of chooser data

[pjm17971]

We need to be able to load chooser data async, because in some cases it's not possible to pre-load all the data on a complex form without really slowing down the user experience. This is especially true for pages that are shown in view mode but have inline editing enabled.

cc: FORMS-2 Ability to load chooser data when the chooser is actually edited