Add xb transform to webform block storage so that it works with Experience Builder

Postponed on 📌 Make webform blocks (block.webform.block:*) fully validatable so they can be used in Experience Builder Active .

@penyaskito tricked XB to allowing the block with the following:

block.settings.webform_block:
  type: block_settings
  label: 'Webforms block'
  constraints:
    FullyValidatable: ~

Which is how the block config showed up in XB and the YAML default values storage appeared. Also adding to issue summary.

Added reference to xb transform docs thanks @penyaskito.

✨ Stop assuming default Field Widget settings suffice — add Field Widget settings support to `experience_builder.generated_field_explicit_input_ux: prop_field_definitions` Active might be a blocker for this.

How would that be a blocker?