[Multiselect] Component API

[chloerice]

Let's nail down the component's API 🔨 We'll discuss things like:

• Which a11y spec should we reference based on the design decisions we've made while prototyping?
• What (if any) state should be managed internally? What should be managed with callback props?

[chloerice]

I love this combobox example because it implements multiple features that are missing from the current autocomplete component, like auto-selection and typeahead.

I think these features and the functionality in general should be controlled outside of the component with render props (e.g.,renderOption) and other callbacks. Dictating the shape of the data or the expected content is too prescriptive, as we've learned from a number of our components, from DataTable to Button.

We've been prototyping in web for easy testing with spin within existing implementations of multiselect autocomplete inputs in the Admin, namely within the TagCard on detail views of things like orders and products. Let's continue the prototyping we've done with Combobox and Listbox in this repo so we can share publicly as we try on different API approaches.

[chloerice]

We've aligned on adding a new "searchable multi select with inline autocomplete" pattern to the Admin based on the example linked above. However, we'll be holding off on implementing this pattern as a new Multiselect component in the system for now. We'll instead update tag management examples across component docs with the new pattern as a deliverable of this project. We'll build the component within web and release behind a beta flag in order to quickly iterate based on merchant feedback as we rollout.