[0035] Rework enumerations and type handling

This change seeks to address a few issues relating to the enumerations
defined in the spec. Some of these are cosmetic, but there is one
functional change. A recent conversation we decided (at least for our
initial preview) to disallow elementwise operations for types that are
not natively representable in HLSL. There is a small header change and
spec wording to adjust to that.

The remaining changes here separate the linalg::ComponentType enum from
the dxil::ComponentType enum. The enumerations are named the same and
their values match, but the linalg::ComponentType is a subset of the
dxil::ComponentType enum to allow only the valid cases through the
header. I've also updated the spec to detail validation requirements at
the DXIL level to enforce only valid values.

Fixes #569, Fixes #730, Fixes #779, Fixes # 798

Author: llvm-beanz