This exposes makes the dialog API usable for users of Goa. It turns the
former static dialog library to a shared object and accompanied symbols
file, and adds depot recipes for the library and API.
Issue #5409
The new API at gems/include/dialog/ aids the creation of simple GUI
applications based on the menu-view widget renderer. Its use is
illustrated by the simple test application at src/test/dialog/
that is accompanied with the dialog.run script.
Issue #5008