[MicroBenchmarks] Add benchmarks to check runtime of truncate or zero-extend vector operations

This patch adds an initial set of benchmarks to check runtime of vectorized truncate or
zero-extend operations in a loop for different vector types over different vector widths.

The goal of this initial benchmark is to check the impact of AArch64 specific changes in
D133495, D135229 and D120571.

Differential Revision: https://reviews.llvm.org/D136274