[Ada] Fix slices and qualified expressions being effectively volatile
gcc/ada/
* exp_ch5.adb (Expand_Assign_Array): Use short-circuit operator
(style).
* sem_res.adb (Resolve_Indexed_Component): Fix style in comment.
* sem_util.adb (Is_Effectively_Volatile_Object): Handle slices
just like indexed components; handle qualified expressions and
type conversions lie in Is_OK_Volatile_Context.
(Is_OK_Volatile_Context): Handle qualified expressions just like
type conversions.