Initial work to add Elementor widget versions of our core page shortcodes

[kimcoleman]

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Changes proposed in this Pull Request:

This is the start of some work to add Elementor Widget versions of our various shortcodes. This version has mixed rendering the Elementor preview - some preview nicely while others just show as an unrendered shortcode.

That might be ok. Maybe not. Page builder people definitely have ideas of how the visual building experience should function. This is a positive step in the direction of giving them the ability to insert our "things" in their pages.

We can consider to do more work here per-widget to add settings, we could convert PMPro pages from the shortcode to the "widget" when people click "Edit With Elementor" and we detect our shortcode was in use. I'll be writing a pitch related to this exploratory work.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
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