[jit][edge] Use dynamic type instead of union types for schema parsers. (#70509)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70509
TypeFactory will construct DynamicType when building on Edge platforms. We use this facility to make FunctionSchema return DynamicType all the time for OptionalType. We don't explicitly use DynamicTypeFactory everywhere because that requires too many changes and will split the entire aten codebase.
ghstack-source-id: 146818621
Test Plan: CI
Reviewed By: iseeyuan
Differential Revision: D33306737
fbshipit-source-id: d7ce00b438f7c03b43945d578280cfd254b1f634
