Editor: Block render filters are not called on nested blocks

[noisysocks]

First reported here: ​https://github.com/WordPress/gutenberg/issues/25900

pre_render_block, render_block_data and render_block_context are only called for top-level blocks which isn't what you would expect from reading those filters' documentation and likely causes unexpected bugs e.g. that the Latest Posts block does not have its attributes migrated.

We should be applying these filters inside WP_Block::_construct as well.

To test, add these filters and then open a post that has some blocks inside a Group block. Note that the filters aren't called for the inner blocks.

<?php
add_filter(
        'pre_render_block',
        function( $pre_render, $parsed_block ) {
                var_dump( 'pre_render_block', $pre_render, $parsed_block );
        },
        10,
        2
);

add_filter(
        'render_block_data',
        function( $parsed_block, $source_block ) {
                var_dump( 'render_block_data', $parsed_block, $source_block );
        },
        10,
        2
);

add_filter(
        'render_block_context',
        function( $context, $parsed_block ) {
                var_dump( 'render_block_context', $context, $parsed_block );
        },
        10,
        2
);

[noisysocks]

cc. @gziolo

[noisysocks]

Oops, this was already ticketed: #51612

[scruffian]

This was never fixed and the Gutenberg issue is also closed so I think this should be reopened.

[scruffian]

Duplicate of #51612.

oh wait I missed https://core.trac.wordpress.org/ticket/51612, sorry.