Improve linear indexing performance for FastSubArrays (#45371)
This PR forwards `AbstractUnitRange` indices for `FastSubArrays` to the
parent, making use of the fact that the parent might have efficient
vector indexing methods defined.
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Co-authored-by: Jishnu Bhattacharya <jishnub@users.noreply.github.com>
Co-authored-by: N5N3 <2642243996@qq.com>