VideoPress: Transform wpvideo shortcodes to video blocks

It would be great if the VideoPress extension could define a new [transform](https://github.com/Automattic/wp-calypso/blob/d1eda6780c88bbb68c00bcd2643253e417beed7e/client/gutenberg/extensions/videopress/editor.js#L67) for the [wpvideo shortcode](https://en.support.wordpress.com/videopress/).

That way, when opening an old post containing `[wpvideo]` shortcodes (or when pasting them in a new post), they are converted automatically to VideoPress-enhanced video blocks like we do with the [related posts](https://github.com/Automattic/wp-calypso/blob/d1eda6780c88bbb68c00bcd2643253e417beed7e/client/gutenberg/extensions/related-posts/index.js#L65-L68) or [simple payments](https://github.com/Automattic/wp-calypso/blob/d1eda6780c88bbb68c00bcd2643253e417beed7e/client/gutenberg/extensions/simple-payments/index.js#L92-L110) shortcodes.

Only the hd, autoplay and loop shortcode options can be supported by the VideoPress extension so we can probably ignore the rest of them (width, height, freedom).

Start with client/gutenberg/extensions/videopress/editor.js and compare the shortcode transforms in related-posts/index.js and simple-payments/index.js. Implement the wpvideo transform for old and pasted shortcodes, preserving only hd, autoplay, and loop, then verify that it produces VideoPress-enhanced video blocks.

Written by the indexing model from the issue text.