Node sockets have many different aspects that affect their visibility and
whether they are grayed out. This patch cleans up the methods used to check if
sockets are visible and adds descriptions that should make it more obvious which
ones should be used.
This also fixes a few places where the wrong method was used which is more
obvious now.
Pull Request: https://projects.blender.org/blender/blender/pulls/139251
1307137f27