Upgrade to Spring Asciidoctor Extensions 0.4.0.RELEASE

0.4.0 provides built-in support for remembering a user's selections
using local storage. This replaces the custom switch language
JavaScript.

The selection is stored using a key derived from the
options that were available. Concretely, when the options are Java or
Kotlin, the local storage key is java-kotlin. Similarly, if the
choices were Java, Kotlin, and XML, the key would be java-kotlin-xml.

Given local storage's domain and protocol scoping, the nature of the
key that's used for storage will allow a user's selections to be
applied across all documentation hosted on https://docs.spring.io that
offer the same options.

Closes gh-24481

gradle/docs.gradle

@@ -3,7 +3,16 @@ configurations {
 }
 
 dependencies {
-	asciidoctorExt("io.spring.asciidoctor:spring-asciidoctor-extensions:0.2.0.RELEASE")
+	asciidoctorExt("io.spring.asciidoctor:spring-asciidoctor-extensions-block-switch:0.4.0.RELEASE")
+}
+
+repositories {
+	maven {
+		url "https://repo.spring.io/release"
+		mavenContent {
+			group "io.spring.asciidoctor"
+		}
+	}
 }
 
 /**

src/docs/asciidoc/docinfo-footer.html

@@ -1,3 +1,2 @@
 <script type="text/javascript" src="js/tocbot/tocbot.min.js"></script>
 <script type="text/javascript" src="js/toc.js"></script>
-<script type="text/javascript" src="js/switch-language.js"></script>

src/docs/asciidoc/js/switch-language.js

@@ -1,43 +0,0 @@
-function globalSwitch() {
-
-    var SPRING_LANGUAGES = ["Java", "Kotlin"];
-    var preferredLanguage = initPreferredLanguage();
-
-    function initPreferredLanguage() {
-        var lang = window.localStorage.getItem("preferred-spring-language");
-        if (SPRING_LANGUAGES.indexOf(lang) === -1) {
-            window.localStorage.setItem("preferred-spring-language", SPRING_LANGUAGES[0]);
-            lang = SPRING_LANGUAGES[0];
-        }
-        return lang;
-    }
-
-    function switchItem(text, index) {
-        if (SPRING_LANGUAGES.indexOf(text) !== -1) {
-            window.localStorage.setItem("preferred-spring-language", text);
-        }
-        $(".switch--item").filter(function() { return ($(this).text() === text) }).each(function() {
-            $(this).addClass('selected');
-            $(this).siblings().removeClass('selected');
-            var selectedContent = $(this).parent().siblings(".content").eq(index)
-            selectedContent.removeClass('hidden');
-            selectedContent.siblings().addClass('hidden');
-        });
-    }
-
-    $('.switch--item').each(function() {
-        $(this).off('click');
-        $(this).on('click', function() {
-            var selectedText = $(this).text()
-            var selectedIndex = $(this).index()
-            switchItem(selectedText, selectedIndex);
-        });
-    });
-
-    var languageIndex = SPRING_LANGUAGES.indexOf(preferredLanguage);
-    if (languageIndex != 0) {
-        switchItem(preferredLanguage, languageIndex);
-    }
-}
-
-$(globalSwitch);