WishlistIntake: Introduce preSubmitPromises to run things before submit

MusikAnimalrequested to merge
pre-submit-promises into main

VisualEditor needs to sync the contents to the native textarea. Because we're mixing Vue and OOUI, we need a means to track the promise that syncs the content and ensure it is ran before validations and form submission. This MR accomplishes by having DescriptionField bubble up the promise to WishlistIntake as soon as it is called.

The new addPreSubmitPromise() provides a means for anything else to register pre-submission promises, should we ever need it.

Bug: T368539

Merge request reports