Implement @wordpress/html-entities package

[jeffpaul]

Is your enhancement related to a problem? Please describe. As part of the 2.3.4 hotfix release, we merged #53 knowing with more time and less pressure to get a hotfix released there was a more appropriate fix for #44.

Describe the solution you'd like

Per @helen's comment, we should switch to the @wordpress/html-entities package to more fully resolve #43 and see if that will avoid us getting dinged by automated scanners.

Designs

n/a

Describe alternatives you've considered

none.

Additional context

Inherits from #53.