[Meta] [UX] Better permissions UI

I'd like to propose adding a better UI for permissions to Backdrop core. I envisage it working/looking something like the following D7 modules: - Filter permissions - https://github.com/backdrop/backdrop-issues/issues/5796 - Permission Select - Fast Permissions Administration - Permissions Grid

Also, I'd like to have the ability for modules to specify group headings within their permissions. This screenshot shows how the Node permissions might look with this change:

If anyone has other ideas for improving the permissions UI, post them here.

• [ ] #1046 | [UX] Permissions page: Make permission groups rows collapsible/expandable
• [ ] #3815 | [META][UX][DX] Overhaul User module permissions and the respective admin UI