The main goal is to simplify adding support for nested node panels. The patch
makes use of the updated recursive node declarations introduced in
6ffc585fb8.
The main changes are:
* Rewritten node drawing in a way that makes ui design decisions like panel
visibility and margins more explicit. Especially the handling of margins is
much better now imo. Previously, it was very hard to change the margin for
specific cases without accidentally breaking other situations. Now each
possible case has an explicit margin. This needs a few more lines of code but
is much easier to work with.
* Rewritten node drawing in panel (sidebar + material properties) using the new
ways to iterate over the declaration.
* It's possible to add custom layouts at any point in the node declaration now.
This also replaces the need for having a `draw_buttons` callback for panels.
Pull Request: https://projects.blender.org/blender/blender/pulls/128822
a239bfc4dd