[CoreML EP] Implement Unary & Reduce operators (#15532)
### Description
This change is a follow-up to #15327. It adds Unary operators (Sqrt,
Reciprocal) and Reduce operators (ReduceSum, ReduceMean). I've tried to
follow existing patterns in the code :-)
### Motivation and Context
This reduces fragmentation across EPs when using CoreML on macOS,
thereby speeding up execution.
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Co-authored-by: Edward Chen <18449977+edgchen1@users.noreply.github.com>
