Elements preview support, Query improvements

[iansvo]

Required PRs

• https://github.com/tomusborne/gp-premium/pull/548
• https://github.com/EDGE22-Studios/components/pull/16
• https://github.com/tomusborne/generateblocks-pro/pull/795

New

• Added a new filter specifically for REST requests to get-wp-query.
• Added new filter for the context object that previews use to support the forthcoming preview mechanism in GP Elements (https://github.com/tomusborne/gp-premium/pull/548).

Improved

• SelectPostType now supports single or multiple selection.

Fixed

• Post per page editor cap is now correctly enforced.
• Updated Looper renderer to fix error that causes InspectorControls to not render if the Query has no items found.

[tomusborne]

@iansvo Are we hoping to get this into the rc tomorrow? Or do we want to do another beta?

My only concern is the changing of params (noted above).

We need to be careful when changing params, especially filter params. One user got a fatal error when updating to latest Pro while still having older Free, as the number of args in the query filter was no longer correct (just as an example).

[iansvo]

Overall this seems to work great, we had testing done which @diggeddy noted out, all seems pretty solid. There's a small issue with post meta queries which I'd like to resolve in the pro PR before we merge this, should be very easy to do.