Previously, when dropping a node on a link with incompatible sockets, the link
would be removed. While sometimes useful in super simple setup, it is generally
useless for most work. Even worse, users might not notice that they accidentally
removed a link (this has been reported in the recent geometry nodes workshop).
This patch changes this behavior in two ways:
* A node can't be inserted onto an incompatible link anymore.
* A link will be dimmed while dragging a node over it, if it is incompatible or if
alt is pressed.
Pull Request: https://projects.blender.org/blender/blender/pulls/121975
ebb61ef30f