Update ref docs for Inner class names

This commit updates the reference manual to point out that one may use
`.` instead of `$` as the nested class separator when providing a fully
qualified class name for a nested class in XML configuration.

This commit also updates the test for ClassUtils#forName to assert
support for `.` instead of `$`.

Closes gh-26540

Author: alex-krav

spring-core/src/test/java/org/springframework/tests/sample/objects/TestObject.java

@@ -75,4 +75,7 @@ public int compareTo(Object o) {
 			return 1;
 		}
 	}
+
+	public static class NestedObject {
+	}
 }

spring-core/src/test/java/org/springframework/util/ClassUtilsTests.java

@@ -86,6 +86,8 @@ void forName() throws ClassNotFoundException {
 		assertThat(ClassUtils.forName("org.springframework.tests.sample.objects.TestObject[][]", classLoader)).isEqualTo(TestObject[][].class);
 		assertThat(ClassUtils.forName(TestObject[][].class.getName(), classLoader)).isEqualTo(TestObject[][].class);
 		assertThat(ClassUtils.forName("[[[S", classLoader)).isEqualTo(short[][][].class);
+		assertThat(ClassUtils.forName("org.springframework.tests.sample.objects.TestObject$NestedObject", classLoader)).isEqualTo(TestObject.NestedObject.class);
+		assertThat(ClassUtils.forName("org.springframework.tests.sample.objects.TestObject.NestedObject", classLoader)).isEqualTo(TestObject.NestedObject.class);
 	}
 
 	@Test

src/docs/asciidoc/core/core-beans.adoc

@@ -641,15 +641,13 @@ You can use the `Class` property in one of two ways:
 
 ****
 .Inner class names
-If you want to configure a bean definition for a `static` nested class, you have to use
-the binary name of the nested class.
+If you want to configure a bean definition for a `static` nested class, you may use
+either binary name of the nested class or separate it with dot.
 
 For example, if you have a class called `SomeThing` in the `com.example` package, and this
-`SomeThing` class has a `static` nested class called `OtherThing`, the value of the `class`
-attribute on a bean definition would be `com.example.SomeThing$OtherThing`.
-
-Notice the use of the `$` character in the name to separate the nested class name from
-the outer class name.
+`SomeThing` class has a `static` nested class called `OtherThing`, they can be separated
+by a dollar (`$`) or dot (`.`). So the value of the `class` attribute on a bean definition
+would be `com.example.SomeThing$OtherThing` or `com.example.SomeThing.OtherThing`.
 ****