yarn package does not create a reproducible vsix file

[stevedlawrence]

Even when building in the exact same environment and setting SOURCE_DATE_EPOCH, the yarn package does not build a reproducible vsix file.

I think only difference between two vsix files is the timestamps included the the visx/zip format. If we could get whatever zips the extension into a .vsix file to use SOURCE_DATE_EPOCH for these timestamps, this might fix it.