refactor(openxr): make environment blend modes a completely runtime feature, like it should and remove the fb_passthrough plugin from the default oxr plugins as quests now support blendmode based passthrough

Signed-off-by: Schmarni <marnistromer@gmail.com>

crates/bevy_openxr/examples/android/src/lib.rs

@@ -16,6 +16,7 @@ fn main() {
             ..default()
         }))
         .add_plugins(bevy_mod_xr::hand_debug_gizmos::HandGizmosPlugin)
+        .add_plugins(bevy_mod_openxr::features::fb_passthrough::OxrFbPassthroughPlugin)
         .add_systems(Startup, setup)
         .add_systems(Update, modify_msaa)
         .insert_resource(AmbientLight {