nothing should be considered a Pyret value

(cherry picked from commit 16bb5ef66df5cf5e671b5dd388734ae887cd61eb)
numbers don't have methods

(cherry picked from commit b37a32e54a1e4db1ead9ff940b15035b3a93f595)
Passing srclocs as AST expressions down through desugaring to ANF.  Then collecting all the srclocs that are actually used, constructing them once and for all (as compact JS arrays) at the beginning of the module, and simply referencing them as needed in the rest of the code.  Saves ~1.25MB of code size