[AArch64] Zero extended extract_vector_elt pattern

This adds a pattern for i64 zext_inreg(i32 extract_vector_elt X),
producing a single UMOVvi16 instruction that is already expected to
clear the top bits. The exact pattern that this matches is
and(anyext(vector_extract X, lane), 0xff), similar to the sext patterns
higher up in the same file.

Differential Revision: https://reviews.llvm.org/D98599