Merge branch '3490150-2.0.0-rc1-should-stringproptype' into '2.0.x'

...ld_formatters/tests/fixtures/tests.formatter_per_item.yml

src/Plugin/UiPatterns/PropType/AttributesPropType.php

src/Plugin/UiPatterns/PropType/LinksPropType.php

src/Plugin/UiPatterns/PropType/StringPropType.php

src/PropTypeInterface.php

src/PropTypePluginBase.php

src/Template/TwigExtension.php

...st/components/test-component/test-component.component.yml

...tterns_test/components/test-component/test-component.twig

...s/src/Kernel/PropTypeNormalization/StringPropTypeTest.php