Housekeeping 2: Rearrange tests, some refactors, remove massive obsolete fixtures

[dotkas]

• Cleaned up repetitive or non-sensical tests.
• Moved functions into classes suffering from envyness, where a file would be the sole consumer of certain functionality from another file
• Consolidated multiple tests files doing the same thing
• Organized the stubs folder (renamed fixtures to keep in convention with Snyk tests) to not be a clusterfudge of random files and folders but instead ordered under relevant subfolders)
• Removed a few MASSIVE fixtures (~250 files) for both project.assets.json and packages-config with alternate packages resolution that was already covered completely in other tests.

Before:

After:

[snyksec]

:tada: This PR is included in version 1.27.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: