Use unicode characters in docs equations (#3487)

javac and javadoc needed the encoding set to UTF-8.

shared/java/javacommon.gradle

@@ -96,7 +96,12 @@ sourceSets {
 }
 
 tasks.withType(JavaCompile).configureEach {
-    options.compilerArgs = ['--release', '11']
+    options.compilerArgs = [
+        '--release',
+        '11',
+        '-encoding',
+        'UTF8'
+    ]
 }
 
 dependencies {