Shader language "levels": moving forward

In today's call, I think there were some communication gaps regarding the
different "levels" of shading language/format. I think it's valuable to
take such a confusing discussion into email, where we can be more precise.

I think we agree there are roughly 3 possible levels: GLSL/C-level,
text-IR, and binary-IR. For each of these 3 levels we need to eventually
answer these 4 questions, ignoring (if possible) exactly *which* language
is used at each level:

- Should we bless any particular language/format at this level?
- If so, should we spec/test that format?
- If so, should the browser ingest that format?
- If not, should we bless an app-side converter library from that format TO
the ingested format?

It sounds like there's disagreement on these questions right now. So
instead of asking for opinions on these questions immediately, I want to
start with this: Are there issues we can discuss first which inform these
questions? Are investigations or research needed? Are we blocked on "big"
un-agreed-upon questions such as the security model? (If we're blocked,
maybe we can agree to eschew this topic for now.)

(And if it wasn't already meta enough,) If you have anything to add or
modify about anything I've said *in this email*, please bring it up now,
before further discussion to avoid confusion.

-Kai