Improve support for JavaScript component children

[Archmonger]

Current Situation

Currently, JavaScript components are fairly janky in terms of support for having children elements. This includes children that are either server-side or JavaScript components.

This has resulted in usability issues in things such as ReactPy-Material.

Proposed Actions

Test and fix all edge cases for JavaScript component children. Ideally, they should be able to be mix-and-matched with anything, in any order.