Adjust `TestHelper` access, drop use of `@testable import`

[andrewdmontgomery]

Closes #

Description

Since the TestHelper target is not listed as a Product in the Package.swift, it is not available for use by third parties who integrate our SDK.

Instead of using @testable, let's set the access levels in the TestHelper module such that they reflect our usage of the module from the GravatarTests and GravatarUITests modules.

• Stops using@testable import imports when importning TestHelper in the GravatarTests and GravatarUITests unit tests.
• Makes the bare minimum access changes within the TestHelper module to accommodate this change
• Uses package access

Testing Steps

• [ ] All GravatarTests should pass locally
• [ ] All GravatarUITests should pass locally
• [ ] make validate-pod should pass locally (note: there is one warning about deprecation, which CI ignores)
• [ ] You should not be able to import TestHelper from the Demo App
• [ ] CI should be 🟢

[andrewdmontgomery]

I wasn't here when this was created. So I don't know the history. I'll bet there was a reason to @testable import for this originally.

This seems to work well now, though. Is there a reason to continue to use the @testable import still?

[pinarol]

Is there a reason to continue to use the @testable import still?

Nope I don't think there is.