Add thorough tests for debug file chunk uploading

[szokeasaurusrex]

Our current chunk uploading tests don't appear to actually verify that inputting a given file to Sentry CLI for chunk upload produces the expected chunks.

Before refactoring the chunk uploading code to add support for chunk uploading Proguard files, we should add tests that ensure that for a given debug information file, Sentry CLI produces the correct chunks for upload. This way, we can more easily detect if our refactor introduces a change in behavior