compiler: eliminate `Core.Compiler.` qualifier (#52790)
To avoid symbol name clashes, this commit defines and uses
`partialorder(𝕃::AbstractLattice) = ⊑(𝕃)`. While I have a preference for
a 2-arg binary operator for lattice operations, it's currently
coexisting with a 3-arg version, suggesting that a unification might be
beneficial.
