Introduce Freemarker/Velocity/TilesWebMvcConfigurer

This change improves the support for auto-registration of FreeMarker,
Velocity, and Tiles configuration.

The configuration is now conditional not only based on the classpath
but also based on whether a FreeMarkerConfigurer for example is already
present in the configuration.

This change also introduces FreeMarker~, Velocity~, and
TilesWebMvcConfigurer interfaces for customizing each view technology.

The WebMvcConfigurer can still be used to configure all view resolvers
centrally (including FreeMarker, Velocity, and Tiles) without some
default conifguration, i.e. without the need to use the new
~WebMvcConfigurer interfaces until customizations are required.

Issue: SPR-7093

spring-test/src/test/java/org/springframework/test/web/servlet/samples/context/JavaConfigTests.java

@@ -35,6 +35,7 @@ import org.springframework.test.web.servlet.samples.context.JavaConfigTests.WebC
 import org.springframework.test.web.servlet.setup.MockMvcBuilders;
 import org.springframework.web.context.WebApplicationContext;
 import org.springframework.web.servlet.config.annotation.*;
+import org.springframework.web.servlet.view.tiles3.TilesConfigurer;
 
 import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.*;
 
@@ -99,7 +100,7 @@ public class JavaConfigTests {
 
 	@Configuration
 	@EnableWebMvc
-	static class WebConfig extends WebMvcConfigurerAdapter {
+	static class WebConfig extends WebMvcConfigurerAdapter implements TilesWebMvcConfigurer {
 
 		@Autowired
 		private RootConfig rootConfig;
@@ -126,9 +127,13 @@ public class JavaConfigTests {
 
 		@Override
 		public void configureViewResolution(ViewResolutionRegistry registry) {
-			registry.tiles().definition("/WEB-INF/**/tiles.xml");
+			registry.tiles();
 		}
 
+		@Override
+		public void configureTiles(TilesConfigurer configurer) {
+			configurer.setDefinitions("/WEB-INF/**/tiles.xml");
+		}
 	}
 
 }