Remove unchecked indexed set on normal arrays

[dcodeIO]

Turned up in #2575, where if --uncheckedBehavior always is given, an array[index] = ..., when setting an index >= length, does not ensure that the array has enough capacity. Code might however expect that this basic contract holds regardless. Hence this PR removes unchecked indexed set on normal arrays. Does not change fixed sized arrays, where there is no such side-effect to retain.

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