A node would not show the "Collapse/Expand" arrows (caused by
87c011f8bb which moved the drawing code for the input nodes a new
`custom_draw_fn` callback on the socket declaration).
Related fix: 7f07124d30
So in order to resolve, make sure we have correct conditions to show the
expander and also make sure we draw the custo buttons in appropriate
places.
NOTE: not sure if there are better ways to achieve the correct UI split
alignment, since we draw with empty labels, I had to flag with
`UI_ITEM_R_SPLIT_EMPTY_NAME` in the new `custom_draw_fn` callbacks.
Pull Request: https://projects.blender.org/blender/blender/pulls/144993
d7fa455e66