update build java version to 16

[bryanateoan]

Looks like temurin only has 8, 11, and 16. Java 16 is not compatible with the latest versions of spotless and javadoc plugins. spotless has a workaround but we can't use it since we are targeting java 8.

Setting the build workflow to use 11, until our dependencies get updated to 16.

[bryanateoan]

Converting to draft. Looks like spotless has issues with jdk 16 diffplug/spotless#834
tried with 2.12.3 and still get the same error.

[gilday]

We can workaround the Spotless issue, but I have no solution for the incompatibility with the doclet we're using for code samples

<docletArtifact>
  <groupId>org.apidesign.javadoc</groupId>
  <artifactId>codesnippet-doclet</artifactId>
  <version>0.61</version>
</docletArtifact>

It's using internal classes that have been hidden in JDK 16.

There's a JEP for introducing code snippets to the javadoc tool natively (see https://bugs.openjdk.java.net/browse/JDK-8201533). It's slated for JDK 18. I recommend we use only JDK 11 in our build chain (continuing to target JDK 1.8 with the --release javac flag) until JDK 18 at which time we can use the native code snippet support.