feat(16.2-01): host plugin field type elements in the admin SPA

- loadFieldTypes fetches GET /field-types after sign-in, loads each script
  once and adds the styles as global links activateStyles never disables
- PluginField creates the type's element, sets the value property and the
  contract attributes, takes summer-change as the form value and never
  writes back a value the element just emitted
- rendererForField and isRegisteredField route any field with an element
  to PluginField in forms, previews and the save payload
- rebuilt modules/boardwalk/dist

admin/src/components/form/formState.ts

@@ -3,7 +3,7 @@
 import type { AdminRecord, ErrorBody, FormField } from '../../api/types'
 import { permissionValues } from './control'
 import { isMLFieldType, localeRecord } from './mlLocale'
-import { isRegistered } from './registry'
+import { isRegisteredField } from './registry'
 
 export { ML_LOCALE_CHANGE, broadcastMLLocale, isMLFieldType, localeRecord } from './mlLocale'
 
@@ -53,7 +53,7 @@ export function contextAllows(field: FormField, mode: FormMode): boolean {
 export function editablePayload(fields: FormField[], values: AdminRecord, mode: FormMode = 'create'): AdminRecord {
   const out: AdminRecord = {}
   for (const field of fields) {
-    if (field.readOnly || !isRegistered(field.type)) {
+    if (field.readOnly || !isRegisteredField(field)) {
       continue
     }
     const value = values[field.name]