Support accessing constants from imported programs in submodule contexts

[mohammadfawaz]

Description

There are two related use cases involving constants from imported programs that are not currently supported:

1. Accessing a constant from a submodule of an imported program — e.g., child.aleo::submodule::CONST_NAME
2. Accessing an imported program's constant from within a submodule of the current program — i.e., using child.aleo::CONST_NAME inside a local submodule file

Accessing a top-level constant from an imported program (child.aleo::CONST_NAME) already works from the main program file.