Add MSAA interaction note to GLSL_EXT_fragment_shader_barycentric

[stu-s]

[stu-s]

@jekstrand FYI

[gfxstrand]

We should probably also say something about whether or not you can use qualifiers. From today's meeting, I think that's still a tad unclear so we may need to wait until we've confirmed what different implementations support.

[stu-s]

Yeah, I think that we should wait a bit with the qualifier stuff. I wasn't sure whether it was worth pushing this bit now, since it's "better than nothing", and then tweaking it once we've sorted out qualifiers?

[gfxstrand]

Yeah, that's fine with me I guess, as long as we don't close the internal issue until both pieces are resolved.

[gfxstrand]

I submitted a Vulkan spec MR which adds a note there: https://github.com/KhronosGroup/Vulkan-Docs/pull/1881 Would you mind updating this one to also talk about qualifiers? I can't update other people's GitHub PRs.

[gfxstrand]

Looks good to me.

[stu-s]

@johnkslang I think this PR is good to go now.

[stu-s]

@johnkslang @gnl21 Is anyone able to sign this off and merge it, please?