`delete arr[i]` leaves a hole/gap in the array

Various gadgets described require arrays with holes (e.g. [`Array.prototype.shift`](https://github.com/ericcornelissen/pp-runtime-gadgets/blob/061c19b098f33bc20b33f0d4debcf7e614c9421e/pocs/ArrayPrototypeShift-%3Cn%3E.PoC-2.js)). One (unexpected) way these may be introduced at runtime is with a `delete` of an index in the array.

I came across this while reading [The Essence of JavaScript](https://arxiv.org/abs/1510.00925), in particular Figure 3:

```javascript
function sum(arr) {
var r = 0;
for (var i = 0; i < arr["length"]; i = i + 1) {
r = r + arr[i] };
return r };

sum([1,2,3]); // 6
var a = [1,2,3,4];
delete a["3"];
sum(a); // NaN
```

The issue points to pocs/ArrayPrototypeShift-.PoC-2.js and demonstrates the behavior with the delete a["3"] example. Start by reading that PoC and the repository structure; the issue does not specify a target file, tests, or acceptance criteria, so completion would first require defining how this case should be represented.

Written by the indexing model from the issue text.