refactor assert_close to be more modular (#67794)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67794
This change is needed to conveniently use the same comparison mechanism for our internal testsuite (see #67796). The reworked version is on par with the previous version except for the ability to pass a custom message as callable. Before we converted everything to a tensor so it was fairly easy to provide consistent mismatch diagnostics to the callable. Now, with arbitrary `Pair`'s that are used for comparison that is no longer viable.
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D32532206
Pulled By: mruberry
fbshipit-source-id: dc847fba6a795c1766e01bc3e88b680a68287b1e
