Block Bindings: Expose bindable attributes through an annotation in the block definition

[zaguiini]

What problem does this address?

As a plugin developer, there is currently no way of knowing whether or not a block attribute is bindable.

My current workaround is to hard code the list of known bindable attributes, but that might soon get outdated.

What is your proposed solution?

Add a new annotation to the block attribute definition explicitly stating that the attribute is bindable. Something like bindable: boolean.

[gziolo]

There is a slightly related prior exploration from @retrofox for exposing the list of allowed blocks and attributes from the source:

• Block Bindings: set allow blocks list from source handler #60335

@fabiankaegy described how we can build on top of the idea shared in this issue to open dynamic blocks for overrides/bindings:

• Open up "Pattern Overrides" and therefore intern block bindings to custom dynamic blocks #64870

[artemiomorales]

If we use role: content to determine which attributes are bindable, would we still need a bindable: boolean flag?

If we go with role: content as the bindings enabler, I imagine some developers would want the ability to opt content attributes out of block bindings. To address this, one option is to use the flag, though perhaps creating a list and accompanying filter for NOT_ALLOWED_BLOCKS could be a better approach.