Update the Build a Pluggable Widget How-To

[weirdwater]

Small updates to the how-to guides for building a pluggable widget.

[ConnorLand]

Thank you for the code updates @weirdwater . Care to sum up their impact to a Tech Writer? (Just out of curiosity).

[weirdwater]

Sure! Since the last time these snippets were updated some changes were made with respect to the configuration of widget building.

• We now require a newer version of node and npm. Making the --legacy-peer-deps info box obsolete and confusing.
• The React configuration changed, making the createElement import redundant. If you copy the old snippets the widget builder will complain about it.
• I updated some of the snippets to show more context of a change, but continue to communicate what is important with a highlight.