[dart2js] value range analysis very slow for many list accesses.

[rakudrama]

It is unusual for a method to have thousands of indexing expression off the same list, but when it does, compilation can be very slow.

The root cause is that inserting RangeConversion instructions can be quadratic in straight-line code, but on top of that, there is another N multiplier in how the usedBy list is updated, removing each updated use one at a time.