Add support for package access modifier to DependencyClient macro

[ivanlisovyi]

Context

Hey folks 👋 It seems like the @DependencyClient macro doesn't support the package access modifier when generating init's, which makes it harder to split the interface and implementation into two separate targets if the interface uses package access. This is because the generated init will have internal access.

Changes

• Added package access modifier support to DependencyClientMacro
• Added unit test to verify the change

[mbrandonw]

Thanks for the contribution, and thanks for adding a test!