Favor JSR-107 provider if present

Previously, native cache libraries were favored over a standard JSR-107
implementation. If a user has a working setup using JCache with one
provider and switch to another provider, his setup may be broken if we
happen to provide a native support for the new provider.

We now consistently favor JSR-107 if it is present. Native support can
still be enabled via the `spring.cache.type` property.

Closes gh-3822

spring-boot-samples/spring-boot-sample-cache/pom.xml

@@ -33,6 +33,15 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-actuator</artifactId>
 		</dependency>
+
+		<!-- JSR-107 API (uncomment to try the JCache support) -->
+		<!--
+		<dependency>
+			<groupId>javax.cache</groupId>
+			<artifactId>cache-api</artifactId>
+		</dependency>
+		-->
+		
 		<!-- Additional cache providers (uncomment to try them) -->
 		<!--
 		<dependency>