Add convenience methods to Messager

Summary

Add convenience default methods to Messager to make printing common errors, warnings, and notes easier.

Problem

The most common usage patterns of Messager in annotation processors, such as printing a simple error or warning message, are unnecessarily verbose.

Solution

Add convenience default methods to Messager for the most common cases.

Specification

--- a/src/java.compiler/share/classes/javax/annotation/processing/Messager.java
+++ b/src/java.compiler/share/classes/javax/annotation/processing/Messager.java
@@ -39,7 +39,8 @@ import javax.lang.model.element.*;
  * javax.tools.Diagnostic.Kind#ERROR error kind} will {@linkplain
  * RoundEnvironment#errorRaised raise an error}.
  *
- * <p>Note that the messages &quot;printed&quot; by methods in this
+ * @apiNote
+ * The messages &quot;printed&quot; by methods in this
  * interface may or may not appear as textual output to a location
  * like {@link System#out} or {@link System#err}.  Implementations may
  * choose to present this information in a different fashion, such as
@@ -97,4 +98,90 @@ public interface Messager {
                       Element e,
                       AnnotationMirror a,
                       AnnotationValue v);
+    /**
+     * Prints an error.
+     *
+     * @implSpec
+     * The default implementation is equivalent to {@code
+     * printMessage(Diagnostic.Kind.ERROR, msg)}.
+     *
+     * @param msg  the message, or an empty string if none
+     * @since 18
+     */
+    default void printError(CharSequence msg) {
+        printMessage(Diagnostic.Kind.ERROR, msg);
+    }
+
+    /**
+     * Prints an error at the location of the element.
+     *
+     * @implSpec
+     * The default implementation is equivalent to {@code
+     * printMessage(Diagnostic.Kind.ERROR, msg, e)}.
+     *
+     * @param msg  the message, or an empty string if none
+     * @param e    the element to use as a position hint
+     * @since 18
+     */
+    default void printError(CharSequence msg, Element e) {
+        printMessage(Diagnostic.Kind.ERROR, msg, e);
+    }
+
+    /**
+     * Prints a warning.
+     *
+     * @implSpec
+     * The default implementation is equivalent to {@code
+     * printMessage(Diagnostic.Kind.WARNING, msg)}.
+     *
+     * @param msg  the message, or an empty string if none
+     * @since 18
+     */
+    default void printWarning(CharSequence msg) {
+        printMessage(Diagnostic.Kind.WARNING, msg);
+    }
+
+    /**
+     * Prints a warning at the location of the element.
+     *
+     * @implSpec
+     * The default implementation is equivalent to {@code
+     * printMessage(Diagnostic.Kind.WARNING, msg, e)}.
+     *
+     * @param msg  the message, or an empty string if none
+     * @param e    the element to use as a position hint
+     * @since 18
+     */
+    default void printWarning(CharSequence msg, Element e) {
+        printMessage(Diagnostic.Kind.WARNING, msg, e);
+    }
+
+    /**
+     * Prints a note.
+     *
+     * @implSpec
+     * The default implementation is equivalent to {@code
+     * printMessage(Diagnostic.Kind.NOTE, msg)}.
+     *
+     * @param msg  the message, or an empty string if none
+     * @since 18
+     */
+    default void printNote(CharSequence msg) {
+        printMessage(Diagnostic.Kind.NOTE, msg);
+    }
+
+    /**
+     * Prints a note at the location of the element.
+     *
+     * @implSpec
+     * The default implementation is equivalent to {@code
+     * printMessage(Diagnostic.Kind.NOTE, msg, e)}.
+     *
+     * @param msg  the message, or an empty string if none
+     * @param e    the element to use as a position hint
+     * @since 18
+     */
+    default void printNote(CharSequence msg, Element e) {
+        printMessage(Diagnostic.Kind.NOTE, msg, e);
+    }
 }