winex11.drv: Preparation for nulldrv display modes.

Merged Rémi Bernon requested to merge rbernon/wine:mr/nulldrv into master

The idea is to have a add_mode manager callback and enumerate adapter modes when updating display devices. Then the modes would be read from the registry and cached with the adapters and monitors, allowing us to move more things to win32u.

This MR is a preparation towards that, moving the winex11 settings handler to display.c, and making sure we do not enumerate display modes before they have been initialized or while the list is being built.

Merge request reports