Support for Custom Declarations in MSIX

Support for custom declarations has been added in MSIX project.

By default, the Declarations view in MSIX project supports many built-in application and package extension types. In addition to this, a Custom Declaration feature further helps to define the MSIX extensions that are not provided out of the box in InstallShield. The Custom Declaration menu provides the options to define the required extension type by specifying its namespace and the content. InstallShield build process considers these customizations while preparing the MSIX manifest file. For more information and examples, refer to InstallShield product documentation.