[feature request] support run-end encoded layout

The Arrow spec has a "run-end encoded layout" (https://arrow.apache.org/docs/format/Columnar.html#run-end-encoded-layout) but it doesn't appear to be supported in Arrow.jl. Seems fairly straightforward to implement since the `run_ends` and `values` arrays are "child arrays" and not buffers, so we could "just" re-use teh existing functionality to represent the values and run-ends.

Start with the Arrow specification's run-end encoded layout section and inspect Arrow.jl's existing functionality for child arrays. The work is done when the run_ends and values child arrays can represent the run-end encoded layout in Arrow.jl.

Written by the indexing model from the issue text.