[@ember/object] add utility-style notifyPropertyChange

[mike-north]

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• Provide a URL to documentation or source code which provides context for the suggested changes: Allow notifyPropertyChange to be imported from @ember/object emberjs/ember.js#17357 (this was missing from docs, and has been public API since ember 3.1)

• Increase the version number in the header if appropriate.
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[typescript-bot]

@mike-north Thank you for submitting this PR!

🔔 @jedmao @bttf @dwickern @chriskrycho @theroncross @mfeckie @alexlafroscia @BryanCrotaz - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

[typescript-bot]

Since you're a listed owner and the build passed, this PR is fast-tracked. A maintainer will merge shortly. If it shouldn't be merged yet, please leave a comment saying so and we'll wait. Thank you for your contribution to DefinitelyTyped!