XWIKI-17421: Import code base from Mentions application

xwiki-platform-core/pom.xml

xwiki-platform-core/xwiki-platform-mentions/pom.xml

...iki-platform-mentions/xwiki-platform-mentions-api/pom.xml

...c/main/java/org/xwiki/platform/mentions/DisplayStyle.java

...ain/java/org/xwiki/platform/mentions/MentionLocation.java

...g/xwiki/platform/mentions/MentionNotificationService.java

...va/org/xwiki/platform/mentions/MentionsConfiguration.java

...java/org/xwiki/platform/mentions/events/MentionEvent.java

...rg/xwiki/platform/mentions/events/MentionEventParams.java

...xwiki/platform/mentions/script/MentionsScriptService.java

...m-mentions-api/src/main/resources/META-INF/components.txt

...platform-mentions/xwiki-platform-mentions-default/pom.xml

.../mentions/internal/DefaultMentionNotificationService.java

...platform/mentions/internal/DefaultMentionXDOMService.java

...tform/mentions/internal/DefaultMentionsConfiguration.java

.../xwiki/platform/mentions/internal/MentionXDOMService.java

...atform/mentions/internal/MentionsConfigurationSource.java

...tform/mentions/internal/async/MentionsCreatedRequest.java

...atform/mentions/internal/async/MentionsCreatedStatus.java

...tform/mentions/internal/async/MentionsUpdatedRequest.java