`adw_init` shouldn't forcibly change back the stylesheet to Adwaita if another is set that is not Default

Currently, calling adw_init to initialize Libadwaita always changes the used stylesheet to "Adwaita", even if the user has set it to another non-default, custom GTK4 stylesheet.

Shouldn't this maybe work more like it did in GTK3 instead? This won't cause a problem if Default/Adwaita is already used, and if it is different, have styling for the needed Libadwaita widgets, however don't change everything. And if the theme stylesheet has support for libadwaita widgets, like a few gtk3 stylesheets did, it looks good, however if it doesn't it just looks awful, and that should be the user's problem, however atleast the stylesheet isn't completely ignored.

This can be useful in situations where it is extremely expected that changing the stylesheet actually affects the application (or like for immediately seeing if it works), and so it wouldn't be weird that standard GTK4 apps follow the stylesheet, but apps that use Libadwaita (which is growing very quickly), don't follow it for seemingly no reason. Also, many people will probably not understand why their custom stylesheets seemingly "stopped working" in 41, and will still try to change it.

Also, I am aware of the existence of https://stopthemingmy.app