Add a build profile for JDK 16 (#10675)

Motivation:
Java 16 will come around eventually anyway, and this makes it easier for people to experiment with Early Access builds.

Modification:
- Added Maven profiles for JDK 16 to relevant pom files.
- Removed the `--add-exports java.base/sun.security.x509=ALL-UNNAMED` argument when running tests; we've not needed it since the Java11-as-baseline PR landed.

Result:
Netty now builds on JDK 16 pre-releases (provided they've not broken compatibility in some way).

handler-proxy/pom.xml

@@ -28,8 +28,6 @@
 
   <properties>
     <javaModuleName>io.netty.handler.proxy</javaModuleName>
-    <!-- Needed for SelfSignedCertificate -->
-    <argLine.java9.extras>--add-exports java.base/sun.security.x509=ALL-UNNAMED</argLine.java9.extras>
   </properties>
 
   <name>Netty/Handler/Proxy</name>

handler/pom.xml

@@ -28,8 +28,6 @@
 
   <properties>
     <javaModuleName>io.netty.handler</javaModuleName>
-    <!-- Needed for SelfSignedCertificate -->
-    <argLine.java9.extras>--add-exports java.base/sun.security.x509=ALL-UNNAMED</argLine.java9.extras>
   </properties>
 
   <name>Netty/Handler</name>

pom.xml

@@ -97,6 +97,31 @@
         <testJvm/>
       </properties>
     </profile>
+    <!-- JDK16 -->
+    <profile>
+      <id>java16</id>
+      <activation>
+        <jdk>16</jdk>
+      </activation>
+      <properties>
+        <!-- Not use alpn agent as Java11+ supports alpn out of the box -->
+        <argLine.alpnAgent />
+        <argLine.java9.extras />
+        <!-- Export some stuff which is used during our tests -->
+        <argLine.java9>--illegal-access=deny ${argLine.java9.extras}</argLine.java9>
+        <forbiddenapis.skip>true</forbiddenapis.skip>
+        <!-- Needed because of https://issues.apache.org/jira/browse/MENFORCER-275 -->
+        <enforcer.plugin.version>3.0.0-M3</enforcer.plugin.version>
+        <!-- 1.4.x does not work in Java10+ -->
+        <jboss.marshalling.version>2.0.5.Final</jboss.marshalling.version>
+        <!-- This is the minimum supported by Java12+ -->
+        <maven.compiler.source>11</maven.compiler.source>
+        <maven.compiler.target>11</maven.compiler.target>
+        <!-- pax-exam does not work on latest Java12 EA 22 build -->
+        <skipOsgiTestsuite>true</skipOsgiTestsuite>
+      </properties>
+    </profile>
+
     <!-- JDK15 -->
     <profile>
       <id>java15</id>
@@ -893,7 +918,7 @@
       <plugin>
         <groupId>org.apache.felix</groupId>
         <artifactId>maven-bundle-plugin</artifactId>
-        <version>2.5.4</version>
+        <version>5.1.1</version>
         <executions>
           <execution>
             <id>generate-manifest</id>

testsuite/pom.xml

@@ -107,8 +107,6 @@
   </dependencies>
 
   <properties>
-    <!-- Needed for SSL tests as these use the SelfSignedCertificate --> 
-    <argLine.java9.extras>--add-exports java.base/sun.security.x509=ALL-UNNAMED</argLine.java9.extras>
     <skipJapicmp>true</skipJapicmp>
   </properties>
 

transport-blockhound-tests/pom.xml

@@ -50,13 +50,27 @@
         <argLine.common>-XX:+AllowRedefinitionToAddDeleteMethods</argLine.common>
       </properties>
     </profile>
+    <profile>
+      <id>java15</id>
+      <activation>
+        <jdk>15</jdk>
+      </activation>
+      <properties>
+        <argLine.common>-XX:+AllowRedefinitionToAddDeleteMethods</argLine.common>
+      </properties>
+    </profile>
+    <profile>
+      <id>java16</id>
+      <activation>
+        <jdk>16</jdk>
+      </activation>
+      <properties>
+        <argLine.common>-XX:+AllowRedefinitionToAddDeleteMethods</argLine.common>
+      </properties>
+    </profile>
   </profiles>
 
   <properties>
-    <maven.compiler.source>11</maven.compiler.source>
-    <maven.compiler.target>11</maven.compiler.target>
-    <!-- Needed for SelfSignedCertificate -->
-    <argLine.java9.extras>--add-exports java.base/sun.security.x509=ALL-UNNAMED</argLine.java9.extras>
     <skipJapicmp>true</skipJapicmp>
   </properties>
 

transport-native-epoll/pom.xml

@@ -28,8 +28,6 @@
 
   <properties>
     <javaModuleName>io.netty.transport.epoll</javaModuleName>
-    <!-- Needed as we use SelfSignedCertificate in our tests -->
-    <argLine.java9.extras>--add-exports java.base/sun.security.x509=ALL-UNNAMED</argLine.java9.extras>
     <unix.common.lib.name>netty-unix-common</unix.common.lib.name>
     <unix.common.lib.dir>${project.build.directory}/unix-common-lib</unix.common.lib.dir>
     <unix.common.lib.unpacked.dir>${unix.common.lib.dir}/META-INF/native/lib</unix.common.lib.unpacked.dir>

transport-native-kqueue/pom.xml

@@ -353,8 +353,6 @@
 
   <properties>
     <javaModuleName>io.netty.transport.kqueue</javaModuleName>
-    <!-- Needed as we use SelfSignedCertificate in our tests -->
-    <argLine.java9.extras>--add-exports java.base/sun.security.x509=ALL-UNNAMED</argLine.java9.extras>
     <unix.common.lib.name>netty-unix-common</unix.common.lib.name>
     <unix.common.lib.dir>${project.build.directory}/unix-common-lib</unix.common.lib.dir>
     <unix.common.lib.unpacked.dir>${unix.common.lib.dir}/META-INF/native/lib</unix.common.lib.unpacked.dir>