Improved default transforms for vdom_to_html

[Archmonger]

Description

This PR predominantly is to backport the improved vdom_to_html transforms from reactpy-django into reactpy.

Changelog

• Renamed reactpy.utils.html_to_vdom to reactpy.utils.string_to_reactpy.
• Renamed reactpy.utils.vdom_to_html to reactpy.utils.reactpy_to_string.
• reactpy.utils.string_to_reactpy has been upgraded to handle more complex scenarios without causing ReactJS rendering errors.
• reactpy.utils.reactpy_to_string will now retain the user's original casing for element data-* and aria-* attributes.
• Convert pragma: no cover comments to nocov

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

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