Fix javadoc build (#1866)

With newer versions of Java 11, javadoc fails to build due to unknown
tags in package-info.java files. These files are not important so we
exclude them.

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build.gradle

@@ -528,6 +528,10 @@ task javaIncrementalFormatApply {
 
 task javadoc(type: Javadoc) {
   source javadocSource
+  // Java 11.0.17 has the following bug that affects annotation handling on
+  // package-info.java:
+  // https://bugs.openjdk.org/browse/JDK-8222091
+  exclude "**/package-info.java"
   classpath = files(javadocClasspath)
   destinationDir = file("${buildDir}/docs/javadoc")
   options.encoding = "UTF-8"