Make SpEL's OptimalPropertyAccessor private

It was never necessary for SpEL's OptimalPropertyAccessor to be public.

Instead, clients should interact with OptimalPropertyAccessor
exclusively via the CompilablePropertyAccessor API.

In light of that, this commit makes SpEL's OptimalPropertyAccessor
private.

Closes gh-32410

Author: sbrannen

spring-expression/src/main/java/org/springframework/expression/spel/support/ReflectivePropertyAccessor.java

@@ -504,15 +504,16 @@ protected Field findField(String name, Class<?> clazz, boolean mustBeStatic) {
 	}
 
 	/**
-	 * Attempt to create an optimized property accessor tailored for a property of a
-	 * particular name on a particular class. The general ReflectivePropertyAccessor
-	 * will always work but is not optimal due to the need to lookup which reflective
-	 * member (method/field) to use each time read() is called. This method will just
-	 * return the ReflectivePropertyAccessor instance if it is unable to build a more
-	 * optimal accessor.
-	 * <p>Note: An optimal accessor is currently only usable for read attempts.
+	 * Attempt to create an optimized property accessor tailored for a property
+	 * of a particular name on a particular class.
+	 * <p>The general {@link ReflectivePropertyAccessor} will always work but is
+	 * not optimal due to the need to look up which reflective member (method or
+	 * field) to use each time {@link #read(EvaluationContext, Object, String)}
+	 * is called.
+	 * <p>This method will return this {@code ReflectivePropertyAccessor} instance
+	 * if it is unable to build a optimized accessor.
+	 * <p>Note: An optimized accessor is currently only usable for read attempts.
 	 * Do not call this method if you need a read-write accessor.
-	 * @see OptimalPropertyAccessor
 	 */
 	public PropertyAccessor createOptimalAccessor(EvaluationContext context, @Nullable Object target, String name) {
 		// Don't be clever for arrays or a null target...
@@ -597,19 +598,20 @@ public int compareTo(PropertyCacheKey other) {
 
 
 	/**
-	 * An optimized form of a PropertyAccessor that will use reflection but only knows
-	 * how to access a particular property on a particular class. This is unlike the
-	 * general ReflectivePropertyResolver which manages a cache of methods/fields that
-	 * may be invoked to access different properties on different classes. This optimal
-	 * accessor exists because looking up the appropriate reflective object by class/name
-	 * on each read is not cheap.
+	 * An optimized {@link CompilablePropertyAccessor} that will use reflection
+	 * but only knows how to access a particular property on a particular class.
+	 * <p>This is unlike the general {@link ReflectivePropertyAccessor} which
+	 * manages a cache of methods and fields that may be invoked to access
+	 * different properties on different classes.
+	 * <p>This optimized accessor exists because looking up the appropriate
+	 * reflective method or field on each read is not cheap.
 	 */
-	public static class OptimalPropertyAccessor implements CompilablePropertyAccessor {
+	private static class OptimalPropertyAccessor implements CompilablePropertyAccessor {
 
 		/**
 		 * The member being accessed.
 		 */
-		public final Member member;
+		private final Member member;
 
 		private final TypeDescriptor typeDescriptor;