Cleanup distillation

[Kmeakin]

Miscellaneous cleanups/refactors of surface::distillation:

• Replace the mutually recursive check and synth functions with a single term function. Now all logic is contained in one single function, and is IMO easier to understand.
• Boolean patterns were erroneously distilled to name patterns instead of boolean patterns in the surface syntax
• Avoid allocating an intermediate Vec when distilling a function application to a binop

[brendanzab]

Nice cleanups!