py: Downcase all MP_OBJ_IS_xxx macros to make a more consistent C API.

These macros could in principle be (inline) functions so it makes sense to
have them lower case, to match the other C API functions.

The remaining macros that are upper case are:
- MP_OBJ_TO_PTR, MP_OBJ_FROM_PTR
- MP_OBJ_NEW_SMALL_INT, MP_OBJ_SMALL_INT_VALUE
- MP_OBJ_NEW_QSTR, MP_OBJ_QSTR_VALUE
- MP_OBJ_FUN_MAKE_SIG
- MP_DECLARE_CONST_xxx
- MP_DEFINE_CONST_xxx

These must remain macros because they are used when defining const data (at
least, MP_OBJ_NEW_SMALL_INT is so it makes sense to have
MP_OBJ_SMALL_INT_VALUE also a macro).

For those macros that have been made lower case, compatibility macros are
provided for the old names so that users do not need to change their code
immediately.

py/objfloat.c

@@ -174,7 +174,7 @@ STATIC mp_obj_t float_unary_op(mp_unary_op_t op, mp_obj_t o_in) {
 STATIC mp_obj_t float_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     mp_float_t lhs_val = mp_obj_float_get(lhs_in);
 #if MICROPY_PY_BUILTINS_COMPLEX
-    if (MP_OBJ_IS_TYPE(rhs_in, &mp_type_complex)) {
+    if (mp_obj_is_type(rhs_in, &mp_type_complex)) {
         return mp_obj_complex_binary_op(op, lhs_val, 0, rhs_in);
     } else
 #endif