[DEMO]: MAAS UI List Tree Fix

[jmuzina]

Done

This PR includes the changes from #5270, as well as updates to the custom styling from MAAS UI so that their .p-list-tree--static can be made compatible with our changes to the list tree.

This PR should NOT be merged into Vanilla - it is purely for demonstrative purposes for MAAS UI devs.

Note: this is based on #5270, so includes its changes. The interesting stuff is this:

  // MAAS UI static tree styling (`.p-list-tree--static`)
  .p-list-tree--static {
    // Force the entire tree to be visible
    display: block !important;

    // Replace expand button with collapse button
    // This is only needed if you are running a script, like react components, that changes the `aria-hidden` of the `.p-list-tree`.
    .p-list-tree--static::before {
      @extend %list-tree-collapse-icon;
    }
  }

and the lack of toggling aria-hidden on .p-list-tree elements with JS for the maas tree example.

Screenshots

[webteam-app]

Demo

Jenkins

demos.haus