Merge branch '3501914-2.0.0-rc3-found-miss' into '2.0.x'

Issue #3501914 by grimreaper: [2.0.0-rc3] Config schema: third party settings for slot source.

See merge request !330

modules/ui_patterns_field_formatters/config/schema/ui_patterns_field_formatters.sources.schema.yml

@@ -8,3 +8,11 @@ ui_patterns_source.field_formatter:*:*:*:
     settings:
       type: field.formatter.settings.[%parent.type]
       label: 'Field formatter settings'
+    third_party_settings:
+      # Third party settings are always optional: they're an optional extension
+      # point.
+      requiredKey: false
+      type: sequence
+      label: 'Third party settings'
+      sequence:
+        type: field.formatter.third_party.[%key]