[LV] Cache call vectorization decisions (#66521)

LoopVectorize currently queries VFDatabase repeatedly for each CI,
and each query to VFDatabase rescans all vector variants.

This patch instead makes a decision for each call once per VF based
on the cost of scalarization vs. function call to a vector variant
of the function vs. a vector intrinsic, then caches the decision
along with relevant info for use in planning and plan execution.