use pxtc.decodeBase64 instead of atob in worker (#3802)
use pxtc.decodeBase64 instead of atob in worker (#3802)


switch-education/pxt,Microsoft/pxt,playi/pxt,switch-education/pxt,Microsoft/pxt,playi/pxt,switch-education/pxt,playi/pxt,Microsoft/pxt,switchinnovations/pxt,switchinnovations/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,switch-education/pxt,switchinnovations/pxt,playi/pxt,switchinnovations/pxt