Fix for Stickers AppExtensions: fails to complete Apple Store validation

Event after fixing signature case apple keeps rejecting applications with Stickers app extension with message:

Invalid iMessage App - Your iMessage app contains an invalid sticker pack. The app may have been built or signed with non-compliant or prerelease tools. For more information, go to developer.apple.com.

user @sofroma investigated case and has found that Xcode additionally copies support files into Apple store package. The package was missing following files:

• MessagesApplicationExtensionSupport/MessagesApplicationExtensionStub
• MessagesApplicationSupport/MessagesApplicationStub

These files are part of iPhoneOS platform and available as part of Xcode at following location: /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Application Support

The fix is to copy these file during packing ipa, check this commit for details.
Sadly these files are part of XCode and can’t be used on Windows/Linux in corresponding RoboVM port