This patch improves warnings displayed when the user attempts to use
passes in render engines other than EEVEE with the viewport compositor.
Previously, an error icon was always displayed if the viewport
compositor was in use as well as a viewport overlay text. This error
existed even when the render engine was set to EEVEE and even if the
passes are not actually used, which was always confusing for users.
This patch improves this by only displaying the error when a pass is
actually used and when a non-EEVEE render engine is used.
This is implemented internally as an extra info callback for the node.
And the compositor_unsupported_message member hack was removed.
Pull Request: https://projects.blender.org/blender/blender/pulls/144005
d84d779661