Apply SingleSpaceSeparator Checkstyle module

This commit also fixes its violations.

Closes gh-31469

spring-aop/src/main/java/org/aopalliance/intercept/ConstructorInterceptor.java

@@ -43,7 +43,7 @@ import javax.annotation.Nonnull;
  *
  * @author Rod Johnson
  */
-public interface ConstructorInterceptor extends Interceptor  {
+public interface ConstructorInterceptor extends Interceptor {
 
 	/**
 	 * Implement this method to perform extra treatments before and

spring-aop/src/main/java/org/springframework/aop/aspectj/AbstractAspectJAdvice.java

@@ -307,7 +307,7 @@ public abstract class AbstractAspectJAdvice implements Advice, AspectJPrecedence
 				this.discoveredReturningType = ClassUtils.forName(name, getAspectClassLoader());
 			}
 			catch (Throwable ex) {
-				throw new IllegalArgumentException("Returning name '" + name  +
+				throw new IllegalArgumentException("Returning name '" + name +
 						"' is neither a valid argument name nor the fully-qualified " +
 						"name of a Java type on the classpath. Root cause: " + ex);
 			}
@@ -342,7 +342,7 @@ public abstract class AbstractAspectJAdvice implements Advice, AspectJPrecedence
 				this.discoveredThrowingType = ClassUtils.forName(name, getAspectClassLoader());
 			}
 			catch (Throwable ex) {
-				throw new IllegalArgumentException("Throwing name '" + name  +
+				throw new IllegalArgumentException("Throwing name '" + name +
 						"' is neither a valid argument name nor the fully-qualified " +
 						"name of a Java type on the classpath. Root cause: " + ex);
 			}