Issue #3438973 by pfrenssen, ayalon, dulnan: Port WebformElementValidationMultiple to GraphQL 4

...gin/GraphQL/DataProducer/WebformElementMultipleValues.php

src/Plugin/GraphQL/DataProducer/WebformElementProperty.php

src/Plugin/GraphQL/DataProducer/WebformElements.php

src/Plugin/GraphQL/Fields/Element/WebformElementMultiple.php

.../GraphQL/Fields/Element/WebformElementValidationLimit.php

src/Plugin/GraphQL/SchemaExtension/WebformExtension.php

...Plugin/GraphQL/Types/WebformElementValidationMultiple.php

src/WebformSchemaBuilder.php

...fig/install/webform.webform.graphql_webform_test_form.yml

tests/queries/multiple.gql

tests/src/Kernel/DataProducer/WebformElementPropertyTest.php

tests/src/Kernel/Element/MultipleValuesTest.php

tests/src/Kernel/Element/TextFieldTest.php