Block bindings: Add filter for supported block attributes

[maxschmeling]

Adds a filter called block_bindings_supported_block_attributes to allow adding blocks / attributes to the supported list.

This list of allowed attributes for block bindings is the only thing in core keeping us from making larger use of block bindings for our Remote Data Blocks plugin. The bindings already work how we need them to, they just aren't allowed on custom blocks, and this filter will allow us to add additional blocks / attributes to the list so we can hook remote data up to dynamic blocks using the standard block binding functionality.

For our use case, the use of this will be abstracted away by our plugin and it would not be super problematic to deprecate this filter if another approach is decided on in the future. But without this change making it into 6.7, it means our RDB plugin will be severely limited in functionality until at least 6.8, so getting this merged would be huge for us.

Trac ticket: https://core.trac.wordpress.org/ticket/62090

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[github-actions]

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[github-actions]

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