RequireThis rule and fixThis Gradle task

* `gradlew clean check -x test --parallel --continue` - to collect reports
* `gradlew fixThis --parallel` - to fix all possible vulnerabilities. With `-Dfile.encoding=UTF-8` on Windows

Since the `RequireThisCheck` doesn't see parents for anonymous classes (e.g. `Runnable` callback), its report doesn't contains the outer class name with `this.`,
therefore we still have to fix those cases manually.
Thanks to the wrong `replacer` just with `this.` we have uncompilable code enough easy to find problems.
Not so easy to fix for good readability though...

* Upgrade to Grade 2.12
* Upgrade to SonarQube native plugin

The fix contains at about 300 files. So, will be done on merge.

Fix `fixThis.gradle` according PR comments

Apply `fixThis` and also `fixModifiers` for test classes.
 Fix some `this.` inner issues manually.
 Make code polishing for long lines after `fixThis`

Fix conflicts and vulnerabilities after the rebase

spring-integration-http/src/test/java/org/springframework/integration/http/inbound/HttpRequestHandlingMessagingGatewayTests.java

@@ -427,7 +427,7 @@ public class HttpRequestHandlingMessagingGatewayTests extends AbstractHttpInboun
 
 	private static class TestHttpMessageConverter extends AbstractHttpMessageConverter<Exception> {
 
-		public TestHttpMessageConverter() {
+		TestHttpMessageConverter() {
 			setSupportedMediaTypes(Arrays.asList(MediaType.ALL));
 		}