[GlobalISel][Localizer] Enable intra-block localization of already-local uses.

This changes the localizer to attempt intra-block localizer of instructions
that have local uses. This is useful because sometimes the entry block itself
has many uses of constant-like instructions, which would benefit from shortening
live ranges. Previously if an inst had no non-local uses, we wouldn't add it to
the list of instructions to attempt further intra-block localization.

This gives a 0.7% geomean code size improvement on CTMark.

Differential Revision: https://reviews.llvm.org/D75555