Issue #3620327: Add the raw shape and make an unmapped field visible instead of silent

Every field of a bundle is exposed. A field whose type no shape claimed is answered with the raw value Drupal holds and is queued as needing a shape of its own, so the trade is visible rather than merely made.

• The raw fallback shape, with anything unserializable removed rather than fatal. It declares no field types: being the fallback is a decision of the planner and the engine, not a wildcard in a declaration.
• MyrestFieldExposure answers both exceptions to "every field is exposed" - the black list by name and by pattern, and the include_unmapped switch.
• MyrestUnmappedFieldRecorder keeps the queue in the state, one entry per bundle, field and type.
• Both settings and the queue are on the settings page, so that what is hidden and what is missing a shape can be seen and changed.
• The scan summary counts fields by plugin where the shapes are passed to it.
• The file shape answers with the caption and the display flag of the item.

Closes #3620327