Missing htmlSafe, and isHtmlSafe Redux

[jherdman]

This is not entirely a duplicate of #235 per se, but possibly related.

I had a production app break recently with a deprecated import { htmlSafe } from '@ember/string' usage. Though this import is deprecated, it's not slated for removal until Ember v4. We tracked the problem down to ember-data v3.24 using @ember/string v1 which is being used in prod instead of Ember Source's.

Is it possible to add these missing functions with a deprecation warning and backport?

[jeradg]

Here's a minimal reproducible example of the bug mentioned by @jherdman.

jeradg/ember-prod-test-spike@1a24746

[ef4]

#235 (comment)

[kategengler]

I added versions of these methods that error with explanation in #367