feat: Rendered code view in Template output

[CuriousLearner]

Description

Add Template Output tab just beside Template Source to display the HTML source for the page. This could be helpful for editors to build new designs. This is how it looks:

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have added an appropriate CHANGELOG entry

[mtrythall]

@CuriousLearner I can't really test this without seeing it in a working project, and that's a mess. If you feel good here just merge this, please.