mypy

f0c78c14 - [mypyc] Generate names lazily when pretty-printing IR or generating C (#9767)

[mypyc] Generate names lazily when pretty-printing IR or generating C (#9767) Instead of generating names for ops when building IR, we now generate names immediately before pretty-printing or generating C. This simplifies `Environment` and reduces the amount of mutable state we need to maintain. This a step towards removing the `mypyc.ir.ops.Environment` class. Also move code related to pretty-printing to `mypyc.ir.pprint`. Work on mypyc/mypyc#781.