Upgrade dependencies including Gradle

* Fix compatibility with upgraded dependencies
* Move `What's New` for `5.4` to `history`
* Add `XmlUnit` dependency since the latest AssertJ has deprecated its `isXmlEqualTo()`
* Remove `javax.annotation-api` and `apiguardian-api` as redundant dependencies

src/checkstyle/checkstyle.xml

@@ -78,6 +78,7 @@
 		<module name="AvoidStaticImport">
 			<property name="excludes"
 					  value="org.assertj.core.api.Assertions.*,
+					  org.xmlunit.assertj3.XmlAssert.*,
 				org.assertj.core.api.Assumptions.*,
 				org.awaitility.Awaitility.*,
 				org.mockito.Mockito.*,