Support @NumberFormat as a meta-annotation

This commit ensures that @NumberFormat can be used as a
meta-annotation, as was already the case for @DateTimeFormat.

In addition, this commit polishes FormattingConversionServiceTests and
MvcNamespaceTests.

Issue: SPR-12743

spring-context/src/main/java/org/springframework/format/annotation/NumberFormat.java

@@ -24,7 +24,8 @@ import java.lang.annotation.Target;
 
 /**
  * Declares that a field should be formatted as a number.
- * Supports formatting by style or custom pattern string.
+ *
+ * <p>Supports formatting by style or custom pattern string.
  * Can be applied to any JDK {@code java.lang.Number} type.
  *
  * <p>For style-based formatting, set the {@link #style} attribute to be the desired {@link Style}.
@@ -41,7 +42,7 @@ import java.lang.annotation.Target;
  */
 @Documented
 @Retention(RetentionPolicy.RUNTIME)
-@Target({ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER})
+@Target({ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
 public @interface NumberFormat {
 
 	/**