Enhancement: PBR Shader: Enable $blendtintbymraoalpha by default

[lenship2]

What would this enhancement be for?

Rendering

Describe your enhancement suggestion in more detail

In the PBR shader, there exists a parameter that enables tint masking using the mrao alpha channel. This originally was based off of the inverted alpha channel, where full alpha mrao maps were untintable, and vice-versa. However, as of a relatively recent update, this behavior was inverted. This means that full alpha mrao maps are now fully tintable.

This behavior makes the parameter practically obsolete however. Most (if not all) mrao maps that exist are going to have a full alpha channel already if the asset creator doesn't care about tinting, so enabling this parameter in most vmts now wouldn't break the behavior of tinting. Old vmts that use the older behavior would likely be the only materials affected by this change, but they're already broken due to the inverting of mrao alpha behavior.

Therefore, I think this behavior should be enabled by default and the parameter should arguably be removed, as I can't think of a single situation where a material designer would deliberately want to disable it.

[JJL772]

This is a good point. For textures without an alpha channel, the shader will read color.a as 1.0 as well.