Introduce "adapters"

Goals

• Being able to write adaptors that can perform BE logic and adapt Drupal field values to match props

Non-goals

• Good UX
• Any UI to change the expression used for a sourceType == dynamic prop value
• Nested adapters
• Translations
• API representation (JSON:API) or otherwise

MR contents

• ** New Adapter plugin type and AdapterManager service **. Each plugin can:
  1. addInput(string $input, mixed $itemBase) - adds input to adapter instance
  2. adapt() - adapts output
  3. outputSchemaMatch($schema) - checks if $schema matches output schema of the adaptor

Tests (minimal)

• ✅ Kernel