Previously, there was the issue that `SocketValueVariant` had a constructor that
took a forwarding reference as parameter. This was problematic, because this
could potentially hide copy/move constructors which is not intentional. This
patch makes sure that these special constructors are not overridden and adds two
static utility functions to make sure it's still straight forward to construct
the `SocketValueVariant` on a single line.
Clangd also warned about this case.
Pull Request: https://projects.blender.org/blender/blender/pulls/140842
ea618c2027