fix: only ignore DEBUG conditional compilation

[cgrindel]

When evaluating whether a source file has a certain import, we will only ignore imports in conditional compilation blocks if it is keying off of DEBUG.

• Add RxSwift to the ios_sim example.
• Update swift_files.has_import() to only ignore code in a conditional compilation block if the evaluator is DEBUG.

Closes #791.

[jpsim]

Thanks for looking into this!

However I think this is incorrectly marking https://github.com/pointfreeco/swift-dependencies as testonly.

[cgrindel]

However I think this is incorrectly marking https://github.com/pointfreeco/swift-dependencies as testonly.

@jpsim Do you know which target?

[cgrindel]

Do you know which target?\

Nevermind. Found it.

[cgrindel]

Instead of trying to configure targets based upon their import of XCTest, we are going to use always_include_developer_search_paths once this PR is merged.