[doc] Rule doc: add maximum language version

Fixes #4140

pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleDocGenerator.java

@@ -392,6 +392,12 @@ public class RuleDocGenerator {
                         lines.add("");
                     }
 
+                    if (rule.getMaximumLanguageVersion() != null) {
+                        lines.add("**Maximum Language Version:** "
+                                + rule.getLanguage().getName() + " " + rule.getMaximumLanguageVersion().getVersion());
+                        lines.add("");
+                    }
+
                     lines.addAll(EscapeUtils.escapeLines(toLines(stripIndentation(rule.getDescription()))));
                     lines.add("");
 

pmd-doc/src/test/resources/expected/sample.md

@@ -155,6 +155,8 @@ Avoid jumbled loop incrementers - its usually a mistake, and is confusing even i
 
 **Minimum Language Version:** Java 1.5
 
+**Maximum Language Version:** Java 11
+
 Override both `public boolean Object.equals(Object other)`, and `public int Object.hashCode()`, or override neither.
 Even if you are inheriting a `hashCode()` from a parent class, consider implementing hashCode and explicitly
 delegating to your superclass.

pmd-doc/src/test/resources/rulesets/ruledoctest/sample.xml

@@ -89,7 +89,8 @@ public class Bar {
           message="Ensure you override both equals() and hashCode()"
           class="net.sourceforge.pmd.lang.java.rule.errorprone.OverrideBothEqualsAndHashcodeRule"
           externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_sample.html#overridebothequalsandhashcode"
-          minimumLanguageVersion="1.5">
+          minimumLanguageVersion="1.5"
+          maximumLanguageVersion="11">
       <description>
             Override both `public boolean Object.equals(Object other)`, and `public int Object.hashCode()`, or override neither.
             Even if you are inheriting a `hashCode()` from a parent class, consider implementing hashCode and explicitly