[3.x] Use the popover API for the progress bar

[pascalbaljet]

The error modal was upgraded to native <dialog> in v3 to avoid z-index issues. This PR does the same for the progress bar by using popover="manual", which promotes the element to the top layer and eliminates the need for z-index hacks.

When the popover API is not supported, the progress bar falls back to the previous z-index: 1031 approach. A popover option is available in createInertiaApp to force either behavior:

createInertiaApp({
  progress: { popover: false },
  // ...
})

The positionUsing setting has been removed since translate3d is now always used.