Add packaging configurations for QtWebAssembly in Qt 5.13 release

Add QtWA in our installers.

• Online only or do we need add WA in offline installers as well?
  • Answer: Online only is fine
• Which binaries located in the installer UI? (will there be x86, armv7 or something else?)
  • Similarly to other platforms, the files that are installed in the build should be included.
  • WebAssembly is actually the architecture, as well as the platform (a sort of bytecode).
• Where to install it?
  • Same as all other platforms, under a subdirectory containing a bin/ lib/ etc.
• Licensing is GPL and Enterprise. Under which enterprise license we will share WA?
  • Answered in comments
• Development platforms : It should be available Linux and iOS,(? MacOS, android?)
  • Plan is to support Windows, but we can start with macOS and Linux
  • Android and iOS are not development platforms.
• Release test automation, what needs to be tested by RTA?
  • This is currently under investigation, so just check the package contents at this point
• Documentation only in the wiki
  • What about examples?
  • Documentation migration is ongoing and examples is just the regular Qt examples (this is a platform)