add support for SPV_EXT_optnone

[bashbaug]

Specifically:

• Updates SPIR-V headers to the latest tag, to pull in support for SPV_EXT_optnone (and more).
• Removes all internal enums for SPV_INTEL_optnone and uses the support in the headers instead.
• Registers the SPV_EXT_optnone extension.
• Uses the SPV_EXT_optnone extension if it is enabled, otherwise uses the SPV_INTEL_optnone extension if it is enabled, otherwise ignores the OptimizeNone attribute (the ignoring part is not new).
• Updates the OptNone test:
  • Ensures that the right extension support is declared, depending on the enabled extensions.
  • Ensures that the OptNone capability is declared when either extension is enabled. Note, the spelling for the capability is unconditionally the EXT version.
  • Ensures that the Function Control is present when either extension is enabled.