py: Add mp_raise_type helper macro and use it where appropriate.

This provides a more consistent C-level API to raise exceptions, ie moving
away from nlr_raise towards mp_raise_XXX.  It also reduces code size by a
small amount on some ports.

extmod/modbtree.c

@@ -256,7 +256,7 @@ STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
         key.data = (void*)mp_obj_str_get_data(index, &key.size);
         int res = __bt_delete(self->db, &key, 0);
         if (res == RET_SPECIAL) {
-            nlr_raise(mp_obj_new_exception(&mp_type_KeyError));
+            mp_raise_type(&mp_type_KeyError);
         }
         CHECK_ERROR(res);
         return mp_const_none;
@@ -266,7 +266,7 @@ STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
         key.data = (void*)mp_obj_str_get_data(index, &key.size);
         int res = __bt_get(self->db, &key, &val, 0);
         if (res == RET_SPECIAL) {
-            nlr_raise(mp_obj_new_exception(&mp_type_KeyError));
+            mp_raise_type(&mp_type_KeyError);
         }
         CHECK_ERROR(res);
         return mp_obj_new_bytes(val.data, val.size);

extmod/modurandom.c

@@ -154,7 +154,7 @@ STATIC mp_obj_t mod_urandom_choice(mp_obj_t seq) {
     if (len > 0) {
         return mp_obj_subscr(seq, mp_obj_new_int(yasmarang_randbelow(len)), MP_OBJ_SENTINEL);
     } else {
-        nlr_raise(mp_obj_new_exception(&mp_type_IndexError));
+        mp_raise_type(&mp_type_IndexError);
     }
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_urandom_choice_obj, mod_urandom_choice);

extmod/moduzlib.c

@@ -61,7 +61,7 @@ STATIC int read_src_stream(TINF_DATA *data) {
         mp_raise_OSError(err);
     }
     if (out_sz == 0) {
-        nlr_raise(mp_obj_new_exception(&mp_type_EOFError));
+        mp_raise_type(&mp_type_EOFError);
     }
     return c;
 }