Optimize getCommandsInPath, restore cache, clean up cache lifecycle, add test

[Tyriar]

Changes:

• Fix cache mechanism as pathValue never got stored
• Cache labels instead of returning empty set
• Walking each directory in separate promise and await via Promise.all
• Don't create a promise on Windows when checking exe
• Move path executable logic into own file and class to help manage lifecycle/testing
• Add a test to prevent future breakages like we've had in the past

Fixes #239396

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First request didn't change too much, but should in the worse case as it's no longer sequential:

Second before (~150ms):

Second after (~8ms):

[meganrogge]

👏🏼