decorator-transforms (https://github.com/ef4/decorator-transforms) is a modern replacement for babel's plugin-proposal-decorators. It provides a decorator implementation using modern browser features, without needing to enable babel's full suite of class feature transformations. This improves the developer experience and performance.
In local testing with Google's 'tachometer' tool, this reduces Discourse's 'init-to-render' time by around 3-4% (230ms -> 222ms).
It reduces our initial gzip'd JS payloads by 3.2% (2.43MB -> 2.35MB), or 7.5% (14.5MB -> 13.4MB) uncompressed.
This updates the behaviour to match ember-cli-htmlbars, and should take care of the handful of themes which were relying on runtime compilation in tests (see 4425e99bf9)
As of #23867 this is now a real package, so updating the imports to
use the real package name, rather than relying on the alias. The
name change in the package name is because `I18n` is not a valid
name as NPM packages must be all lowercase.
This commit also introduces an eslint rule to prevent importing from
the old I18n path.
For themes/plugins, the old 'i18n' name remains functional.
