Allow internal listeners to unsubscribe when executed (closes DevExpress/testcafe#3652)

[AndreyBelym]

Closes DevExpress/testcafe#3652.

babel-plugin-transform-for-of-as-array caches an array length when transforming for-of cycles:

for(const x of xs)

// Transformed To

for(var _i = 0, _length = xs.length; i < _length; ++i)

It can throw a runtime exception if an element is deleted from the array inside the cycle's body.

babel/plugin-transform-for-of produces a safer transpiled code:

for(const x of xs)

// Transformed To

for(var _i = 0; i < xs._length; ++i)

[testcafe-build-bot]

✅ Tests for the commit a208f5e have passed. See details.