Fix map_rect

[seantalts]

• remove the first argument from calls to map_rect even though all other HOFs have the first argument as the function and don't require explicit template arguments
• add a call_id integer that just increments every time we emit a call to map_rect. I think this was a hack that went in before because we didn't want to modify the old compiler too much; now I'm reproducing that hack in the new compiler in lieu of fixing it because it would require nontrivial changes to Math.