Metalness in DBuffer decals

[CattusEx]

@akaChrisV

looking at the feature request backlog chances seem to be slim anyhow unfortunately… maybe try to sneak in the metalness support as a bug report /fix suggestion. Those seem to have a much bigger chance of moving through the pipeline… One could argue that the current system is actually broken in regards to how decals look on metal so not a big stretch…

Is it possible to release this change to decals as a plugin ?