[NPM][Inliner] Factor ImportedFunctionStats in the InlineAdvisor

When using 2 InlinePass instances in the same CGSCC - one for other
mandatory inlinings, the other for the heuristic-driven ones - the order
in which the ImportedFunctionStats would be output-ed would depend on
the destruction order of the inline passes, which is not deterministic.

This patch moves the ImportedFunctionStats responsibility to the
InlineAdvisor to address this problem.

Differential Revision: https://reviews.llvm.org/D94982