[javadoc] IDEA-285556 Support language injection into snippet

Add an enclosing class for snippets in order not to make users define a class in a snippet code to eliminate syntax errors when the code consists of a set of instructions

GitOrigin-RevId: c6f52f94d51fdc6393c8a9fdc0ddb615e8d37b17

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/javaDoc/SnippetMethod.java

@@ -0,0 +1,6 @@
+/** {<warning descr="'@snippet' tag is not available at this language level">@snippet</warning> :
+ * void f() {}
+ * }
+ */
+class A {
+}