[WIP] use scandir-native instead of readdir

[bengl]

This chops about 20% off the primed cache case.

This is only a demo of what's possible if fs.scandir was present.

Don't merge this PR until fs.scandir exists in Node, and this has been updated to use it (and generally cleaned up).

[coveralls]

Pull Request Test Coverage Report for Build 23

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 78.882%

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Totals
Change from base Build 21:	-0.2%
Covered Lines:	187
Relevant Lines:	221

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💛 - Coveralls

[bengl]

Closing this since qdd uses withFileTypes instead, when available.