Block Hooks: Issue warning about child insertion into semi-incompatible blocks

[ockham]

Early-stage WIP. If a plugin tries to insert a hooked block in a position that (currently) won't work in the editor, we might want to alert them (e.g. via _doing_it_wrong).

Trac ticket: TBD

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[ockham]

cc/ @gziolo

[github-actions]

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[gziolo]

If a plugin tries to insert a hooked block in a position that (currently) won't work in the editor, we might want to alert them (e.g. via _doing_it_wrong).

One thing we discussed, was adding a block supports flag that lets the block author to opt-out from allowing hooking the block on a certain position rather than hardcoding only the list for the core blocks that we know aren't compatible. However, it might be enough to go with the simple solution for now as it clearly applies to very complex blocks that source their content from external sources.