Define `repr()` on IValues (#32232)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32232
Previously, we were using `operator<<` as the default way of printing
IValue constants during serialization. The semantics of `operator<<`
were ill-defined; and this bit us in particular with strings and lack of
quoting.
This PR defines the role of `operator<<`: much like Python `str()`, it
is intended to produce a human-readable-ish representation for
debugging purposes.
This PR also defines a new `repr()` function on IValue that is intended
to produce a valid Python expression that can be used to recreate an
object with the same value. `repr()` is not defined on all IValue kinds
(notably tensors!) for this reason.
Test Plan: Imported from OSS
Differential Revision: D19417036
Pulled By: suo
fbshipit-source-id: c102d509eaf95a28b6a62280bc99ca6f09603de5
