This simplifies the C++ API for making layout panels. Now it is also more similar to the Python API.
`uiLayoutPanel` is like `layout.panel` and `uiLayoutPanelProp` is like `layout.panel_prop`.
Both, `uiLayoutPanel` and `uiLayoutPanelProp`, now exist in two variants. One that takes a label
parameter and one that does not. If the label is passed in, only the panel body layout is returned.
Otherwise, the header and body are returned for more customization.
Pull Request: https://projects.blender.org/blender/blender/pulls/117670
In 13fac109 the node panels got support for individual option button
callbacks, but these were not included in the node editor side bar.
Only the older top-level buttons are drawn there.
The panel structure is currently not accessible in python since it is
part of the `NodeDeclaration` system. To draw node input sockets and
buttons in the correct panel order as they appear on the node, a new
template function `uiTemplateNodeInputs` has been added. This iterates
over declared panels and their contents in the appropriate order and
draws the buttons before sockets in the same panel.
Pull Request: https://projects.blender.org/blender/blender/pulls/116936
