[focusgroupV2] Bikeshed names for the focusgroup itemcontrols modifiers

Focusgroup V2 proposes itemcontrols, with noitemcontrols as its negative counterpart. Review feedback on PR #1488 noted that itemcontrols does not clearly communicate its purpose, on which I agree.

With itemcontrols, focusable controls with focusgroup="none" that descend from any non-active focusgroup item are not considered for sequential focus navigation.

<div focusgroup="toolbar itemcontrols" aria-label="Documents">
  <span tabindex="0">
    Quarterly report
    <button focusgroup="none">Rename</button>
    <button focusgroup="none">Delete</button>
  </span>

  <span tabindex="0">
    Project plan
    <button focusgroup="none">Rename</button>
    <button focusgroup="none">Delete</button>
  </span>
</div>

<button>Upload document</button>

• If focus is on Quarterly report and the user presses Tab, focus moves to its Rename button.
• Pressing Tab again moves focus to its Delete button.
• Pressing Tab again skips the inactive Project plan item and its controls, moving focus to Upload document.
• Directional navigation moves between Quarterly report and Project plan (no change from a focusgroup without this modifier).
• If focus moves to Project plan, its controls become the available through sequential focus navigation.
• Pressing Shift+Tab from "Upload document" restores the previously focused focusgroup item, skipping over any nested controls, as they are only considered "active" when focus is on or within them.

Read the Focusgroup V2 proposal and the review feedback on PR #1488, then compare the proposed itemcontrols and noitemcontrols behavior with clearer naming options. Done means reaching agreement on names that communicate the sequential and directional focus-navigation behavior described in this issue.