Cleanup portal version detection and plumb xdg-portal-required-version flag into upstream

### Confirmation

- [x] I am a [maintainer](https://github.com/orgs/electron/people) of the Electron project. (If not, please create a [different issue type](https://github.com/electron/electron/issues/new/).)

### Description

Followup to https://github.com/electron/electron/pull/49175

Refs https://chromium-review.googlesource.com/c/chromium/src/+/7214586

Allows removing the early detection logic in https://github.com/electron/electron/blob/main/shell/browser/ui/file_dialog_linux_portal.cc but we still need a way to support `xdg-portal-required-version` in the new path `dbus_xdg::RequestXdgDesktopPortal`