Show toast when toggling crop borders

Consistent with reading mode and orientation shortcuts.

app/src/main/java/eu/kanade/tachiyomi/data/preference/PreferencesHelper.kt

@@ -38,8 +38,9 @@ operator fun <T> Preference<Set<T>>.minusAssign(item: T) {
     set(get() - item)
 }
 
-fun Preference<Boolean>.toggle() {
+fun Preference<Boolean>.toggle(): Boolean {
     set(!get())
+    return get()
 }
 
 class PreferencesHelper(val context: Context) {