[X86][Costmodel] `trunc v16i8 to v8i1` can appear after legalization, cost is...

[X86][Costmodel] `trunc v16i8 to v8i1` can appear after legalization, cost is same as for `trunc v8i8 to v8i1`

Note that there are many other missing costs, i'm *only* adding the ones that are queried
from `getReplicationShuffleCost()` for the existing (quite exhaustive) test coverage.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D114070