gh-109287: Desugar inst(X) to op(X); macro(X) = X (#109294)

gh-109287: Desugar inst(X) to op(X); macro(X) = X (#109294)

This makes the internal representation in the code generator simpler: there's a list of ops, and a list of macros, and there's no special-casing needed for ops that aren't macros. (There's now special-casing for ops that are also macros, but that's simpler.)