[NewPassManager] Add assertions when getting statefull cached analysis.

Summary:
Analyses that are statefull should not be retrieved through a proxy from
an outer IR unit, as these analyses are only invalidated at the end of
the inner IR unit manager.
This patch disallows getting the outer manager and provides an API to
get a cached analysis through the proxy. If the analysis is not
stateless, the call to getCachedResult will assert.

Reviewers: chandlerc

Subscribers: mehdi_amini, eraman, hiraditya, zzheng, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72893