Docs: Add documentation for render_block and register_block_type_args to Block Filters

[ndiego]

Fixes #64037

What?

The documentation for Block Filters currently does not mention the register_block_type_args or ender_block/render_block_{block/name} filters, which are some of the most used filters for extending and modifying blocks.

This PR adds brief descriptions and an example for each as well as a few other edits. Further edits will be needed for this page as some of the other filters are missing examples. I will tackle that in a follow-up PR.

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Co-authored-by: ndiego <[email protected]>
Co-authored-by: juanmaguitar <[email protected]>

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[juanmaguitar]

I'm missing some guidance in this page about the mixture of PHP and JS functions.
We could add some brief intro of the type of APIs available for each section (Registration, Frontent, Editor...) and some context for that.

For example, registration happens on both the server and the client, so there are APIs to modify block metadata before registration on both sides, but the editor part only happens on the client, so there are only JS functions to alter this side of the block's management.

This could be helpful for developers to understand (and remember) the possibilities and limitations of these filters.

[ndiego]

For example, registration happens on both the server and the client, so there are APIs to modify block metadata before registration on both sides, but the editor part only happens on the client, so there are only JS functions to alter this side of the block's management.

I added a section about this and also linked to the block registration guide for more info.

[gziolo]

Cool, thank you for improving this document 👍