Relocate DefaultPropertiesPropertySource to `env`

Move `DefaultPropertiesPropertySource` from
`org.springframework.boot` to `org.springframework.boot.env` since
it's not directly tied to `SpringApplication`.

See gh-47232

core/spring-boot-test/src/main/java/org/springframework/boot/test/context/ConfigDataApplicationContextInitializer.java

@@ -16,10 +16,10 @@
 
 package org.springframework.boot.test.context;
 
-import org.springframework.boot.DefaultPropertiesPropertySource;
 import org.springframework.boot.bootstrap.DefaultBootstrapContext;
 import org.springframework.boot.context.config.ConfigData;
 import org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor;
+import org.springframework.boot.env.DefaultPropertiesPropertySource;
 import org.springframework.boot.env.RandomValuePropertySource;
 import org.springframework.context.ApplicationContextInitializer;
 import org.springframework.context.ConfigurableApplicationContext;

core/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -65,6 +65,7 @@ import org.springframework.boot.context.properties.bind.Bindable;
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySources;
 import org.springframework.boot.convert.ApplicationConversionService;
+import org.springframework.boot.env.DefaultPropertiesPropertySource;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextInitializer;
 import org.springframework.context.ApplicationListener;

core/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironment.java

@@ -26,7 +26,6 @@ import java.util.Set;
 import org.apache.commons.logging.Log;
 import org.jspecify.annotations.Nullable;
 
-import org.springframework.boot.DefaultPropertiesPropertySource;
 import org.springframework.boot.bootstrap.BootstrapRegistry.InstanceSupplier;
 import org.springframework.boot.bootstrap.BootstrapRegistry.Scope;
 import org.springframework.boot.bootstrap.ConfigurableBootstrapContext;
@@ -36,6 +35,7 @@ import org.springframework.boot.context.properties.bind.Bindable;
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.boot.context.properties.bind.PlaceholdersResolver;
 import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
+import org.springframework.boot.env.DefaultPropertiesPropertySource;
 import org.springframework.boot.logging.DeferredLogFactory;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.Environment;

core/spring-boot/src/main/java/org/springframework/boot/env/DefaultPropertiesPropertySource.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.boot;
+package org.springframework.boot.env;
 
 import java.util.HashMap;
 import java.util.Map;

core/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java

@@ -71,6 +71,7 @@ import org.springframework.boot.context.event.ApplicationStartedEvent;
 import org.springframework.boot.context.event.ApplicationStartingEvent;
 import org.springframework.boot.context.event.SpringApplicationEvent;
 import org.springframework.boot.convert.ApplicationConversionService;
+import org.springframework.boot.env.DefaultPropertiesPropertySource;
 import org.springframework.boot.testsupport.classpath.ForkedClassPath;
 import org.springframework.boot.testsupport.classpath.resources.WithResource;
 import org.springframework.boot.testsupport.system.CapturedOutput;

core/spring-boot/src/test/java/org/springframework/boot/env/DefaultPropertiesPropertySourceTests.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.boot;
+package org.springframework.boot.env;
 
 import java.util.Collections;
 import java.util.function.Consumer;