Update CI to Java 16

[mp911de]

No description provided.

[mikereiche]

see https://youtrack.jetbrains.com/issue/IDEA-263241 and projectlombok/lombok#2681
(even if not using lombok and disabling the lombok plugin, the problem with lombok exists)

To compile in maven, this needs a number of --add-opens :

          <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>16</source>
                <target>16</target>
                <fork>true</fork>
                <compilerArgs>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED</arg>
                    <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.jvm=ALL-UNNAMED</arg>
                </compilerArgs>
                <annotationProcessorPaths>
                    <path>
                        <groupId>org.projectlombok</groupId>
                        <artifactId>lombok</artifactId>
                        <version>1.18.16</version>
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>

Intellij needs those as well as java.util :

--add-opens=java.base/java.util=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.jvm=ALL-UNNAMED

Runtime -

for java.util.UUID and java.util.Optional
   --add-opens=java.base/java.util=ALL-UNNAMED
 for java.math.BigDecimal and BigInteger
  --add-opens=java.base/java.math=ALL-UNNAMED
 for java.lang.boolean, byte[], Integer
  --add-opens=java.base/java.lang=ALL-UNNAMED  

[mikereiche]

Previously had information from Mark in #1057. Should do that instead of using jvm flags.
#1057

[mp911de]

Let's put this ticket on hold for now. Kotlin and Lombok still have compatibility issues and we can only continue here once both issues are resolved.

[mikereiche]

The issue with UUID still exists apart from Lombok/Intellij issues. The Couchbase CustomConversions does not map very well to Mongo CustomConversions. I'm working on sorting that out.