Investigate efficiency of alternative ACIR-gen for applying predicate to array_get

[TomAFrench]

It would be interesting to compare this against the solution of adding an index offset instead of reading 0 to ensure that we read the correct typed value from the array. This keeps the final value a single witness rather than a quadratic expression so should result in better codegen in later opcodes.

Originally posted by @TomAFrench in #4971 (comment)

We're making every conditional read from an array into a quadratic expression in #4971. This may be resulting in worse-than-necessary acir gen later on as we use these results so it would be useful to compare the alternative.