optimize array growth using over-allocation

[dckc]

Describe

We have identified a requirement for a build-time option to over-allocate arrays by, say, 30%, to avoid quadratic performance from things like Array.push() in a loop.

This is a high priority request. Also tracked as Agoric/agoric-sdk#3012

Why do you think this feature would be useful?
Our customers will most likely expect Array.push() to have similar performance to other engines that have this optimization.

array growth is a spreadsheet with some performance measurements (from @dtribble Fri, Jun 11, 1:05 PM KC time).

Describe alternatives you've considered
not many... just doing nothing, I suppose.

cc @phoddie @kriskowal

[dckc]

@dtribble I guess we'll track this elsewhere.

@phoddie feel free to delete this.