fix(file-list): Stop polluting global environment with core-js

[JakeChampion]

When using Karma programatically I came across issues which were due to core-js polluting the environment. It turns out that all Karma needs from core-js (whilst karma supports node 0.x versions) is Map and Set, switching to the file includes for these minimises the amount of core-js being used :-)

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[JakeChampion]

I signed it!

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