* 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
* chore: rename .eslintrc.js to eslint.config.js
* chore: Rename eslint.config.js to eslint.config.mjs.
* refactor: Migrate ESLint config to new flat format.
* chore: Remove old per-directory and global ignore ESLint config files.
* fix: Allowlist JSDoc tag aliases.
* fix: Don't require @license in tests/*.
* fix: Add NodeJS globals to several files that run under Node.
* chore: Remove now-unneeded ESLint directives in core.
* chore: Remove invalid/unneeded ESLint directives.
* fix: Fix invalid use of `await` outside of an `async` function.
* fix: Improve screenshot error message.
* fix: Update ESLint config file to not warn on existing violations.
* chore: Remove suppressions of rules that weren't triggering.
* chore: Fix package-lock.json.
