cleanup API of AffineTransform

[michaelknoch]

Type of change: cleanup

Motivation (current vs expected behavior)

Based on the conversations in #395 (comment)

Please check if the PR fulfills these requirements

• Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
• There are no dependencies on other PRs or I have linked dependencies through Zenhub
• The commit messages are clean and understandable
• Tests for the changes have been added (for bug fixes / features)

[ephemer]

Hi @michaelknoch, I am approving this because in a sense I do consider it an improvement (assuming that the type we're actually intending to vend is CGAffineTransform and not AffineTransform, which I'm pretty sure is the case).

While reviewing this PR though I can see that there would still be quite a bit of cleanup to do in order to "do it properly", i.e. actually renaming AffineTransform to CGAffineTransform to remove the unused type, removing the other initializers that don't exist in CGAffineTransform (like rotationByDegrees), and moving the initializers that are currently in the CGAffineTransform.swift extension into the type itself (and removing their AffineTransform aliases, e.g. scaleByX... as well).

The above doesn't really need to happen before merging this, again assuming that CGAffineTransform is the type we actually intend to vend here. But to "do it properly" there would still be some work here to be done.

I can see that I made CGAffineTransform.swift in May 2017, and from memory I also started working on this project – at least full time – in May 2017 too. So this must be some of the earliest code in the project 😵