[Feature Request] Support GTK4 theme switching

[nikolowry]

With GTK4's new file chooser grid view (See: https://release.gnome.org/44/) nearing its roll-out with Gnome 44 and Chromium's GTK4 support with the flag --gtk-version=4, it be great to see gtk-dark-mode-switch-fix.patch updated to also accommodate org.freedesktop.appearance.color-scheme.I'd hate to have to choose between auto theme switching and the improved file chooser grid view.

I don't typically code in C++, but was thinking:

• Use GtkCheckVersion(https://github.com/chromium/chromium/blob/f69ece76596ef7c5db931570d102c3284a700ef8/ui/gtk/gtk_compat.h#L45) to conditionally define some new variables to based as args to set_use_dark_colors and set_preferred_color_scheme
• Use Glib to get the value of org.freedesktop.appearance.color-scheme, but I'm not positive because I don't typically code desktop/GTK apps.
• Update what signal is connected for observing color-scheme changes
• Make GTK4 the default version to avoid needing --gtk-version flag

When I have a little downtime I'm going to make an attempt to update your patch for my local Ungoogled Chromium builds