ArnoldShaderUI : Support "linkable" metadata.
ArnoldShaderUI : Support "linkable" metadata.

Values of FALSE disable the creation of nodules in the NodeGraph. We don't map "linkable" to the Plug::AcceptsInputs flag, because even if the parameter can't be linked to a shader output, we should still be able to drive it with expressions, promote it etc.

lucienfostier/gaffer,boberfly/gaffer,boberfly/gaffer,chippey/gaffer,appleseedhq/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,hradec/gaffer,GafferHQ/gaffer,hradec/gaffer,ImageEngine/gaffer,lucienfostier/gaffer,hradec/gaffer,GafferHQ/gaffer,chippey/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,appleseedhq/gaffer,ivanimanishi/gaffer,johnhaddon/gaffer,chippey/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,chippey/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,hradec/gaffer,andrewkaufman/gaffer,ivanimanishi/gaffer,hradec/gaffer,andrewkaufman/gaffer,ivanimanishi/gaffer,boberfly/gaffer,johnhaddon/gaffer,boberfly/gaffer,ivanimanishi/gaffer