Updated SPIR-T for better pretty-printing (esp. OpExtInst), and started deduplicating custom debuginfo.

[eddyb]

Potentially relevant SPIR-T PRs that are included here:

• print: use spv.OpFoo(A: imm, B: ID, C: imm, ...) instead of spv.OpFoo<imms>(IDs). spirt#33
• print: always print attributes inline and with per-attribute #[...] syntax. spirt#35
• print: use OpNames to replace the T1/F2/v3 style, when unambiguous. spirt#36
• Pretty-print OpExtInst using official extinst.*.grammar.json and/or custom Context-registered ones. spirt#45

That last one is the most relevant here, because together with debuginfo deduplication, it causes:

Before	After

Yes, that's the same function (sky_shader::henyey_greenstein_phase), but incomprehensible before.