[VectorUtils] Rework the Vector Function Database (VFDatabase).
This commits is a rework of the patch in
The rework was requested to prevent out-of-tree performance regression
when vectorizing out-of-tree IR intrinsics. The vectorization of such
intrinsics is enquired via the static function isTLIScalarize. For
detail see the discussion in https://reviews.llvm.org/D67572.
Reviewers: uabelho, fhahn, sdesmalen
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D72734