List: Allow collapsing of item groups

[ade10176]

Description

Support collapsing of item groups. Users often have a long list of items in a group. Allowing them to collapse each group will support workflow efficiency.

Acceptance Criteria

Collapse/expand Layers, Tables, or Basemaps independently when clicked
https://codepen.io/nwhittaker-esri/pen/bGxeMVq

Relevant Info

No response

Which Component

List

Example Use Case

No response

Esri team

ArcGIS Field Apps

[nwhittaker]

From #8515 (comment):

One design consideration is that we'd want to style top-level groups differently from nested groups. For example, the Layers and Rivers groups within this prototype.