Ensure compilation tests will run on JDK 16+.

As noted [here](google/compile-testing#222), the change of the default `--illegal-access` from `permit` to `deny` will cause compile-testing tests to fail by default, with messages like this:

```
class com.google.testing.compile.Parser (in unnamed module @0x4114d843) cannot
access class
com.sun.tools.javac.api.JavacTool (in module jdk.compiler) because module
jdk.compiler does not export
com.sun.tools.javac.api to unnamed module @0x4114d843
```

We can work around that by supplying the necessary `--add-opens` flag to the JVM that runs the tests.

RELNOTES=n/a
PiperOrigin-RevId: 362396186

factory/pom.xml

@@ -38,6 +38,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <java.version>1.8</java.version>
     <guava.version>30.1-jre</guava.version>
+    <test.jvm.flag/>
     <truth.version>1.1.2</truth.version>
   </properties>
 
@@ -168,6 +169,14 @@
           </dependency>
         </dependencies>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>2.22.2</version>
+        <configuration>
+          <argLine>${test.jvm.flags}</argLine>
+        </configuration>
+      </plugin>
       <plugin>
         <artifactId>maven-jar-plugin</artifactId>
         <version>3.2.0</version>
@@ -200,4 +209,15 @@
       </plugin>
     </plugins>
   </build>
+  <profiles>
+    <profile>
+      <id>open-modules</id>
+      <activation>
+        <jdk>[9,)</jdk>
+      </activation>
+      <properties>
+        <test.jvm.flags>--add-opens=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED</test.jvm.flags>
+      </properties>
+    </profile>
+  </profiles>
 </project>

value/processor/pom.xml

@@ -40,6 +40,10 @@
     <tag>HEAD</tag>
   </scm>
 
+  <properties>
+    <test.jvm.flags/>
+  </properties>
+
   <dependencies>
     <dependency>
       <groupId>com.google.auto</groupId>
@@ -167,6 +171,14 @@
           </compilerArgs>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>2.22.2</version>
+        <configuration>
+          <argLine>${test.jvm.flags}</argLine>
+        </configuration>
+      </plugin>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-jar-plugin</artifactId>
@@ -232,5 +244,14 @@
         <additionalparam>-Xdoclint:none</additionalparam>
       </properties>
     </profile>
+    <profile>
+      <id>open-modules</id>
+      <activation>
+        <jdk>[9,)</jdk>
+      </activation>
+      <properties>
+        <test.jvm.flags>--add-opens=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED</test.jvm.flags>
+      </properties>
+    </profile>
   </profiles>
 </project>

value/src/it/functional/pom.xml

@@ -33,6 +33,7 @@
   <name>Auto-Value Functional Integration Test</name>
   <properties>
     <exclude.tests>this-matches-nothing</exclude.tests>
+    <test.jvm.flags/>
   </properties>
   <dependencies>
     <dependency>
@@ -149,6 +150,14 @@
           <skip>true</skip>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>2.22.2</version>
+        <configuration>
+          <argLine>${test.jvm.flags}</argLine>
+        </configuration>
+      </plugin>
     </plugins>
   </build>
 
@@ -195,5 +204,14 @@
         <exclude.tests>**/AutoValueJava8Test.java</exclude.tests>
       </properties>
     </profile>
+    <profile>
+      <id>open-modules</id>
+      <activation>
+        <jdk>[9,)</jdk>
+      </activation>
+      <properties>
+        <test.jvm.flags>--add-opens=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED</test.jvm.flags>
+      </properties>
+    </profile>
   </profiles>
 </project>