runtime(java): Recognise all available standard doclet tags

* Complement the tag set with @spec, {@systemProperty},
  {@summary}, @provides, @uses, @hidden, and {@index}.
* Do not hoard all tags under a single highlighting group.
* Skip over nested balanced braces in inline tags.
* Observe that tag names are case sensitive: both {@docRoot}
  and {@inheritDoc} are valid, whereas {@inheritdoc} and
  {@docroot} are not.
* In the @see tag arguments, allow for:
  - module name prefixes (e.g. java.base/java.lang.String);
  - references to arbitrary URI fragments (e.g. ##foo);
  - matching any tag variation arguments on the next line.
* Test directives and tags for Java module declarations.
* Enforce the word end for "module-info" candidates.

References:
https://bugs.openjdk.org/browse/JDK-8226279 (@spec)
https://bugs.openjdk.org/browse/JDK-8214559 ({@systemProperty})
https://bugs.openjdk.org/browse/JDK-8173425 ({@summary})
https://bugs.openjdk.org/browse/JDK-8160196 (@provides & @uses)
https://bugs.openjdk.org/browse/JDK-8073100 (@hidden)
https://bugs.openjdk.org/browse/JDK-8044243 ({@index})
https://docs.oracle.com/en/java/javase/21/docs/specs/javadoc/doc-comment-spec.html
https://github.com/openjdk/jdk/blob/jdk-21-ga/src/jdk.compiler/share/classes/com/sun/source/doctree/DocTree.java

closes: #15652

Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/java_comments.java

@@ -1,7 +1,19 @@
-// VIM_TEST_SETUP unlet! g:java_ignore_javadoc g:java_no_trail_space_error
-// VIM_TEST_SETUP unlet! g:java_no_tab_space_error
-// VIM_TEST_SETUP let [g:java_space_errors,g:java_comment_strings] = [1,1]
-// VIM_TEST_SETUP setlocal spell | highlight link javaCommentStart Todo
+// VIM_TEST_SETUP unlet! g:java_no_tab_space_error g:java_ignore_javadoc
+// VIM_TEST_SETUP unlet! g:java_no_trail_space_error
+// VIM_TEST_SETUP let [g:java_space_errors,g:java_comment_strings]=[1,1]
+
+
+
+
+
+
+
+// VIM_TEST_SETUP setlocal spell fdc=2 fdl=64 fdm=syntax fen
+// VIM_TEST_SETUP highlight link javaCommentStart Todo
+// VIM_TEST_SETUP highlight link javaCommentTitle Underlined
+
+
+
 
 
 
@@ -11,8 +23,10 @@
  * {@snippet file = Snippets.java region = main id = _01}
  * <p>There is no textual representation:
  * {@snippet class = Snippets region = toString id = _02} */
-class CommentsTests
+class CommentsTests implements Comparable<CommentsTests>
 {
+	private CommentsTests() { }
+
 	/** No-op, i. e. no operation.
 	* ({@literal@literal} may be used with {@code .} for contraction.)
 	* @return {@code null} */
@@ -49,6 +63,22 @@ class CommentsTests
 	/** {@return {@code null}, with no-op, i.e. no operation} . . */
 	Void noOp9() { return null; }
 
+	/** {@return the major Java version} @hidden */
+	protected int majorVersion() { return 21; }
+
+	/** {@summary Compares this instance with the passed {@code that}
+	 * instance for order by invoking {@link Integer#compare(int, int)
+	 * compare} and passing it {@code this.majorVersion()} and
+	 * {@code that.majorVersion()} as respective @arguments.}
+	 *
+	 * {@inheritDoc} */
+	@Override public int compareTo(CommentsTests that)
+	{
+		java.util.Objects.requireNonNull(that, "that");
+		return Integer.compare(this.majorVersion(),
+						that.majorVersion());
+	}
+
 	/** Returns an empty string for an @Override annotated method
 	* (see Chapter 9.6.4.4 {@literal @Override} in a Java Language
 	* Specification) overridden from <code>java.lang.Object</code>
@@ -57,15 +87,17 @@ class CommentsTests
 	@Override public String toString() { return ""; }
 }
 
-// javadoc --snippet-path . --source-path . -d /tmp/doc/ -package \
+// javadoc --snippet-path . --source-path . -d /tmp/docs/ -package \
 // 	-tag 'jls:a:See Java Language Specification:' Snippets.java
 /** Snippets for comment tests. */
 class Snippets
 {	/* 	TRAILING BLANKS AND MESSPILLINGS ARE SIGNIFICANT! */
+	private Snippets() { }
+
 	/** The method {@code main} must be declared {@code public}, {@code
 	 * static}, and {@code void}.  It must specify a formal parameter
 	 * whose declared type is array of {@link String}.  Therefore,
-	 * either of the following declarations is acceptable:
+	 * <em>either</em> of the following declarations is acceptable:
 	 * 	{@snippet lang="java":
 	 * // @highlight substring="main" type="italic":
 	 * public static void main(String[] args) { }
@@ -79,9 +111,9 @@ class Snippets
 	public static void main(String[] args) { }
 	// @end 
 
-	/** {@return an empty string}	
+	/** {@return an empty string}
 	 * @see <a href="https://docs.oracle.com/javase/specs/jls/se21/html/jls-3.html#jls-3.10.5">3.10.5 String Literals</a>
-	 * @see Object#toString() */
+	 * @see java.base/java.lang.Object#toString() */
 	// @start region = toString	
 	// @replace substring = '""' replacement = "\u0022\u0022"
 	// @link regex = '\bString' target = java.lang.String type = linkplain :