Enable debug mode when running via 'npm run playground'
Enable debug mode when running via 'npm run playground'

This should be OK because none of the rollup configs will process
lib/initialise.js. So when running via 'npm run playground' and
therefore 'node -r lib/initialise.js' we can detect this and define a
global __debug__ variable, which will be detected by the checks that
normally get replaced out.

See: #643

js-temporal/temporal-polyfill,js-temporal/temporal-polyfill,js-temporal/temporal-polyfill