Add syntax highlighting to Javadoc where necessary

Issue: SPR-8426

org.springframework.context/src/main/java/org/springframework/context/annotation/PropertySource.java

@@ -34,7 +34,7 @@ import java.lang.annotation.Target;
  * uses {@code @PropertySource} to contribute {@code app.properties} to the
  * {@code Environment}'s set of {@code PropertySources}.
  *
- * <pre>
+ * <pre class="code">
  * &#064;Configuration
  * &#064;PropertySource("classpath:/com/myco/app.properties")
  * public class AppConfig {
@@ -62,7 +62,7 @@ import java.lang.annotation.Target;
  * {@code b.properties}, consider the following two configuration classes
  * that reference them with {@code @PropertySource} annotations:
  *
- * <pre>
+ * <pre class="code">
  * &#064;Configuration
  * &#064;PropertySource("classpath:/com/myco/a.properties")
  * public class ConfigA { }
@@ -74,7 +74,7 @@ import java.lang.annotation.Target;
  *
  * The override ordering depends on the order in which these classes are registered
  * with the application context.
- * <pre>
+ * <pre class="code">
  * AnnotationConfigApplicationContext ctx =
  *     new AnnotationConfigApplicationContext();
  * ctx.register(ConfigA.class);
@@ -92,7 +92,7 @@ import java.lang.annotation.Target;
  * the ordering is difficult to predict.  In such cases - and if overriding is important -
  * it is recommended that the user fall back to using the programmatic PropertySource API.
  * See {@link org.springframework.core.env.ConfigurableEnvironment ConfigurableEnvironment}
- * and * {@link org.springframework.core.env.MutablePropertySources MutablePropertySources}
+ * and {@link org.springframework.core.env.MutablePropertySources MutablePropertySources}
  * Javadoc for details.
  *
  * @author Chris Beams

org.springframework.core/src/main/java/org/springframework/core/env/AbstractEnvironment.java

@@ -115,7 +115,7 @@ public abstract class AbstractEnvironment implements ConfigurableEnvironment {
 	 * "D". If the {@code Level2Environment} subclass wished to give property sources C
 	 * and D higher precedence than A and B, it could simply call
 	 * {@code super.customizePropertySources} after, rather than before adding its own:
-	 * <pre>
+	 * <pre class="code">
 	 * public class Level2Environment extends Level1Environment {
 	 *     &#064;Override
 	 *     protected void customizePropertySources(MutablePropertySources propertySources) {
@@ -138,7 +138,7 @@ public abstract class AbstractEnvironment implements ConfigurableEnvironment {
 	 * property sources via the {@link #getPropertySources()} accessor, typically within
 	 * an {@link org.springframework.context.ApplicationContextInitializer
 	 * ApplicationContextInitializer}. For example:
-	 * <pre>
+	 * <pre class="code">
 	 * ConfigurableEnvironment env = new StandardEnvironment();
 	 * env.getPropertySources().addLast(new PropertySourceX(...));
 	 * </pre>

org.springframework.test/src/main/java/org/springframework/mock/env/MockPropertySource.java

@@ -28,7 +28,7 @@ import org.springframework.core.env.PropertySource;
  *
  * The {@link #setProperty} and {@link #withProperty} methods are exposed for
  * convenience, for example:
- * <pre>
+ * <pre class="code">
  * {@code
  *   PropertySource<?> source = new MockPropertySource().withProperty("foo", "bar");
  * }

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/config/annotation/EnableWebMvc.java

@@ -27,7 +27,7 @@ import org.springframework.web.servlet.DispatcherServlet;
  * {@link DispatcherServlet}. Add this annotation to an application @{@link Configuration} class. It will in
  * turn import the @{@link Configuration} class {@link WebMvcConfiguration}, which provides default Spring MVC
  * configuration.
- * <pre>
+ * <pre class="code">
  * &#064;Configuration
  * &#064;EnableWebMvc
  * &#064;ComponentScan(
@@ -42,7 +42,7 @@ import org.springframework.web.servlet.DispatcherServlet;
  * {@link WebMvcConfigurerAdapter} overriding specific methods. Your @{@link Configuration} class and any other
  * Spring bean that implements {@link WebMvcConfigurer} will be detected and given an opportunity to customize 
  * the default Spring MVC configuration through the callback methods on the {@link WebMvcConfigurer} interface.
- * <pre>
+ * <pre class="code">
  * &#064;Configuration
  * &#064;EnableWebMvc
  * &#064;ComponentScan(