Background elements of Dialog/Drawer should be unfocus-able and hidden. Headers in background should not show up in screenreader heaver navigation

[faye-tan]

Environment

• Package version(s): 5.8.2
• Browser and OS versions: Edge, Chrome, MacOS Sonoma 14.4

Feature request

When a Dialog or Drawer is open, the background elements should be un-focusable and hidden. This is backed up by this source and this source. Otherwise, the screenreader cursor could focus on something behind the Dialog/Drawer.

Examples

Currently when navigating by headings (CTRL+OPT+U on Mac) using a screenreader, currently when a Dialog or Drawer is open, the headers in the content underneath the overlay are also included in header navigation, which is unexpected.