[AVX-512] Replace large number of explicit patterns that check for insert_subvector...

[AVX-512] Replace large number of explicit patterns that check for insert_subvector with zero after masked compares with fewer patterns with predicate

This replaces the large number of patterns that handle every possible case of zeroing after a masked compare with a few simpler patterns that use a predicate to check for a masked compare producer.

This is similar to what we do for detecting free GR32->GR64 zero extends and free xmm->ymm/zmm zero extends.

This shrinks the isel table from ~590k to ~531k. This is a roughly 10% reduction in size.

Differential Revision: https://reviews.llvm.org/D38217

llvm-svn: 314133