* refactor(build): Rename "package" gulp task (but not npm script) to "pack"
This is to avoid an issue due to "package" being a reserved word
in JavaScript, and therefore not a valid export identifier.
* refactor(build): Convert gulpfile.js from CJS to ESM.
* refactor(build): Convert scripts/gulpfiles/*.js from CJS to ESM
* fix(build): Fix eslint warning for @license tag in gulpfile.mjs
* chore(build): Remove unused imports
* fix(build): Fix incorrect import of gulp-gzip
* fix(build): Fix incorrect sourcemaps import reference
