Ensure Jitpack compatibility

By default Jitpack builds with Java 11.0.2 and Maven 3.6.1.
Additionally, its read-only `/script/toolchains.xml` file points to at
least one nonexistent JDK home directory. See jitpack/jitpack.io#5795.

These days Error Prone releases are built using JDK 17 and require at
least Maven 3.6.3. Additionally, its `maven-toolchains-plugin`
configuration rejects invalid `toolchains.xml` configurations.

As such this change uses SDKMAN! to configure recent Java and Maven
versions, and modifies the build by disabling Maven Toolchains usage.

jitpack.yml

@@ -0,0 +1,8 @@
+before_install:
+  - mvn -version
+  - source "${HOME}/.sdkman/bin/sdkman-init.sh"
+  - sdk update
+  - sdk install java 17.0.12-tem
+  - sdk use java 17.0.12-tem
+  - sdk install maven 3.9.9
+  - sdk use maven 3.9.9

pom.xml

@@ -246,19 +246,6 @@
         <artifactId>maven-surefire-plugin</artifactId>
         <version>3.1.0</version>
         <configuration>
-          <jdkToolchain>
-            <!--
-            Test against the current default JDK, not the latest JDK a toolchain is registered for. 
-
-            On Error Prone's CI, the JDK we want to run the tests against is installed last, to
-            make it the default on the PATH and for JAVA_HOME:
-            https://github.com/google/error-prone/blob/master/.github/workflows/ci.yml
-
-            See also Guava's similar logic here:
-            https://github.com/google/guava/blob/781068569f0a275ac3c4bce08c9a1fe4d624048a/pom.xml#L20
-            -->
-            <version>${java.specification.version}</version>
-          </jdkToolchain>
           <argLine>
             -Xmx1g
             --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED
@@ -289,13 +276,6 @@
             </jdk>
           </toolchains>
         </configuration>
-        <executions>
-          <execution>
-            <goals>
-              <goal>toolchain</goal>
-            </goals>
-          </execution>
-        </executions>
       </plugin>
     </plugins>
   </build>