LibJS: Avoid double construction in Array.fromAsync

[shannonbooth]

This is a normative change in the array from async proposal, see:

tc39/proposal-array-from-async@49cfde2

It fixes a double construction when Array.fromAsync is given an array
like object.

Two test262 tests will now fail, as they have not (currently) been updated to match the updated spec.

[shannonbooth]

hmm one second, might have just seen an issue

[shannonbooth]

Nevermind, false alarm, I confused myself into thinking I was causing test262 failures, but these are expected failures as they were testing the old behaviour.

[trflynn89]

Minor note on the commit message, we typically format editorial/normative updates like so, linking to the spec commit rather than its PR:

This is a normative change in the Set Methods proposal. See:
https://github.com/tc39/proposal-set-methods/commit/4155e6e

See e.g. 4b0ef6b, 31e555a,

[shannonbooth]

Minor note on the commit message, we typically format editorial/normative updates like so, linking to the spec commit rather than its PR:

This is a normative change in the Set Methods proposal. See:
https://github.com/tc39/proposal-set-methods/commit/4155e6e

See e.g. 4b0ef6b, 31e555a,

Thanks, fixed