Add lexical variable getter and setter blocks to core

[mark-friedman]

Even though the core exports aren't generally supposed to include any blocks, the lexical variable getter and setter blocks are required by the the core fields which define variables.

Note that it might be useful to allow the developer to create their own version of the lexical variable getter and setter blocks and override the default ones.

[SurbhiAgarwal1]

Hi @mark-friedman — I’d like to take this up.

My understanding is that core variable fields/features depend on lexical getter/setter blocks being available, but those blocks are not currently part of the core export path. As a result, consumers importing only core must separately import the lexical blocks.

Proposed approach:

• Re-export or register the default lexical getter/setter blocks from the core entry point (without double registration).
• Expose the default block definitions so consumers can override them if needed.
• Add a small demo/test to confirm that core-only import works and document the override mechanism in the README.

Unless there are specific naming constraints for the default block types, I’ll align with the existing lexical block naming conventions.

Let me know if this direction matches your expectations, and I’ll start working on a PR.