Use Class#componentType() for consistency with arrayType()

Java 12 introduced java.lang.Class#componentType() as a shortcut for
getComponentType().

Since we started using arrayType() in fe5560400c, this commit switches
to componentType() for consistent API usage style.

spring-core/src/test/java/org/springframework/core/ResolvableTypeTests.java

@@ -360,7 +360,7 @@ class ResolvableTypeTests {
 		ResolvableType type = ResolvableType.forField(field);
 		assertThat(type.isArray()).isTrue();
 		assertThat(type.getComponentType().getType())
-			.isEqualTo(((Class) field.getGenericType()).getComponentType());
+			.isEqualTo(((Class) field.getGenericType()).componentType());
 	}
 
 	@Test