core: improvements for setImmediate polyfill
core: improvements for setImmediate polyfill

- try use postMessage first instead of MessageChannel as more
predictable task order in multi-sandbox mode
- make postMessage more safe across sandboxes via random generated
message

istrel/basisjs,basisjs/basisjs,tyanas/basisjs,basisjs/basisjs,fateevv/basisjs,smelukov/basisjs,fateevv/basisjs,smelukov/basisjs,basisjs/basisjs,tyanas/basisjs,smelukov/basisjs,tyanas/basisjs,fateevv/basisjs,istrel/basisjs,istrel/basisjs