Fix devtools package tangle

Fix package tangle in devtools by relocating `DevToolsEnablementDeducer`
to a new `system` package.

Closes gh-18393

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/autoconfigure/OnEnabledDevToolsCondition.java

@@ -19,7 +19,7 @@ package org.springframework.boot.devtools.autoconfigure;
 import org.springframework.boot.autoconfigure.condition.ConditionMessage;
 import org.springframework.boot.autoconfigure.condition.ConditionOutcome;
 import org.springframework.boot.autoconfigure.condition.SpringBootCondition;
-import org.springframework.boot.devtools.DevToolsEnablementDeducer;
+import org.springframework.boot.devtools.system.DevToolsEnablementDeducer;
 import org.springframework.context.annotation.ConditionContext;
 import org.springframework.core.type.AnnotatedTypeMetadata;
 

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/env/DevToolsHomePropertiesPostProcessor.java

@@ -24,7 +24,7 @@ import java.util.Properties;
 import java.util.function.Function;
 
 import org.springframework.boot.SpringApplication;
-import org.springframework.boot.devtools.DevToolsEnablementDeducer;
+import org.springframework.boot.devtools.system.DevToolsEnablementDeducer;
 import org.springframework.boot.env.EnvironmentPostProcessor;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.PropertiesPropertySource;

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/env/DevToolsPropertyDefaultsPostProcessor.java

@@ -23,9 +23,9 @@ import java.util.Map;
 import org.apache.commons.logging.Log;
 
 import org.springframework.boot.SpringApplication;
-import org.springframework.boot.devtools.DevToolsEnablementDeducer;
 import org.springframework.boot.devtools.logger.DevToolsLogFactory;
 import org.springframework.boot.devtools.restart.Restarter;
+import org.springframework.boot.devtools.system.DevToolsEnablementDeducer;
 import org.springframework.boot.env.EnvironmentPostProcessor;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.Order;

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/DefaultRestartInitializer.java

@@ -18,7 +18,7 @@ package org.springframework.boot.devtools.restart;
 
 import java.net.URL;
 
-import org.springframework.boot.devtools.DevToolsEnablementDeducer;
+import org.springframework.boot.devtools.system.DevToolsEnablementDeducer;
 
 /**
  * Default {@link RestartInitializer} that only enable initial restart when running a

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/system/DevToolsEnablementDeducer.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.devtools;
+package org.springframework.boot.devtools.system;
 
 import java.util.Collections;
 import java.util.LinkedHashSet;

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/system/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Devtools system support classes.
+ */
+package org.springframework.boot.devtools.system;