Experiment: WP streaming block parser

[mardelnet]

Summary

This PR experiments with the new WP streaming block parser introduced with WordPress 6.9.

This block parser presents a streaming interface to walk through a document and analyze or modify the block structure. So far, the way of doing that was through the parse_blocks() function. Calling parse_blocks() converts the entire post into a large nested array of block information that contains two copies of every span of HTML from the input . All of this work can lead to some surprisingly heavy parsed documents. Further, because block structure is inherently nested, any code wanting to traverse all of the blocks in a document needs to create its own form of recursion to iterate through the output of parse_blocks(). The block parser was designed for cases where parse_blocks() would otherwise perform unnecessary work.

In this particular experiment, I use the block parser to replace the parse_blocks() function and a (somewhat complex) recursive function in its task of detecting a YouTube player on the current page.

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Testing

1. Embed a YouTube video on any page or post.
2. Check that the /assets/build/lite-yt-embed.js file was enqueued.
3. Remove the video.
4. Now the JS file should not be enqueued.