Enables operators that uses `WM_operator_props_dialog_popup`
or `redo` popup to use layout panels.
Other popups would likely also support layout panels, only
they need to set its dummy panel with `UI_popup_dummy_panel_set`.
Popups don't normally use `Panel`, but that's the type that stores the
layout panel states. Therefore, to use layout panels in a popup, one
currently needs to create a dummy panel whose purpose is to store the
layout panel states for as long as the popup is open.
Alternatively, we could potentially also store the layout panel states
somewhere else in the future for popups, but that might be a more involved
change for now.
See #119519 for an example script that uses layout panels in a popup.
Pull Request: https://projects.blender.org/blender/blender/pulls/119519
aa03646a74