[javadoc] IDEA-285556 Support language injection into snippet

Fix injection for empty snippets. The range to inject is now starts after the colon and ends when the body ends. If no colon exist, then use the whole body as an injection point.

GitOrigin-RevId: c7961f13c30212f52aad45a121bcf11b70ce8f2b

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

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

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

@@ -0,0 +1,8 @@
+/**
+ * A simple program.
+ * {<warning descr="'@snippet' tag is not available at this language level">@snippet</warning> :
+ *
+ * }
+ */
+class A {
+}