Make JpaSort.unsafe operational.

We have offered this method as a way for people to customize an ORDER BY clause beyond a simple property name. For example, someone could use "LENGTH(firstname)" as a function to order by the length of each row's lastname instead of ordering by the lastname itself.

By using the relevant parser and applying a different visitor, this commit make operational a feature that shows little evidence of ever having worked.

See #3172.

spring-data-jpa/pom.xml

@@ -407,8 +407,17 @@
 					<xmlConfigured>aop.xml</xmlConfigured>
 				</configuration>
 			</plugin>
-
-		</plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>17</source>
+                    <target>17</target>
+                    <compilerArgs>--enable-preview</compilerArgs>
+                </configuration>
+            </plugin>
+
+        </plugins>
 	</build>
 
 </project>