Mark sun.misc dependency as optional (#5249)

java/core/pom.xml

@@ -135,6 +135,7 @@
             <Bundle-DocURL>https://developers.google.com/protocol-buffers/</Bundle-DocURL>
             <Bundle-SymbolicName>com.google.protobuf</Bundle-SymbolicName>
             <Export-Package>com.google.protobuf;version=${project.version}</Export-Package>
+            <Import-Package>sun.misc;resolution:=optional,*</Import-Package>
           </instructions>
         </configuration>
       </plugin>