refactor to move runtime1-specific calculations out of dsom and grammar

Need to introduce runtime1 package in schema compiler, and add mixins there that contain the runtime1-specific things such as computation of the ElementRuntimeData and TermRuntimeData data structures, which are specific to Runtime1.

There are many calculations that are specific to Daffodil Runtime1 streaming unparser for example, that can be isolated so that it is clear they are runtime1 specific.