Update size according to the order of entering tree

[Rindbee]

To calculate the size of a control, it is necessary to first calculate the size of the parent control.

Previously, the size was actually calculated on first display, and the call in NOTIFICATION_POST_ENTER_TREE was not necessary. In other words, size is not calculated correctly if it is hidden.

Fixes #77815.

[YuriSizov]

For the record, reduz rejected this change before in #19334.

[Rindbee]

1. because computing size with out of tree controls should never happen,
2. and children nodes receive that notification after the parent, so for cases like this it's needed.

I think the second point pointed out by @reduz is the reason for the need to make changes. The order of receiving the notification NOTIFICATION_POST_ENTER_TREE is the same as the notification NOTIFICATION_READY, both of which are children nodes receive that notification before the parent (both in Node::_propagate_ready()).

godot/scene/main/node.cpp

Line 231 in 0a0132c

notification(NOTIFICATION_POST_ENTER_TREE);

About the first point, _notification() is called in inheritance order. By the time NOTIFICATION_ENTER_TREE reaches Control, all prerequisites for calculating the size have been met, and the first drawing request has even been issued.

[YuriSizov]

The order of receiving the notification NOTIFICATION_POST_ENTER_TREE is the same as the notification NOTIFICATION_READY, both of which are children nodes receive that notification before the parent

Yes, that's the point.

[akien-mga]

Superseded by #78009.