Potential Optimization for interleave/take on RunEndEncoded arrays

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
on #7671 (comment), @brancz points out

It actually throws up a larger design question: Should two extend calls, that end up referencing the same value even continue the "previous" run? As in if we an array that is an REE with the logical values being:

[1, 1, 0, 0, 1, 1]

and the interactions are

arr.extend(0, 2)
arr.extend(4, 6)

should the result be

1. runs: [4], values: [1]
2. runs: [2, 4], values: [1, 1]

Obviously 1) is more optimized, but it would also mean that .extend needs to be able to compare arbitrary values (because it needs to know when to continue vs. start a new run)

Describe the solution you'd like
Consider implementing this optimization

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