Add features extra_asserts and extra_debug_asserts for more asserts

This replaces all debug_asserts with these opt-in asserts

Related: https://github.com/emilk/egui/issues/395

emath/src/rot2.rs

@@ -76,7 +76,7 @@ impl Rot2 {
             c: self.c / l,
             s: self.s / l,
         };
-        debug_assert!(ret.is_finite());
+        crate::emath_assert!(ret.is_finite());
         ret
     }
 }