Provide CryptoError Typealias

[0xTim]

Provide a typealias for CryptoError to point to CryptoKitError to hide the underlying implementation detail

Checklist

• I've run tests to see all new and existing tests pass
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary

If you've made changes to gyb files

• I've run .script/generate_boilerplate_files_with_gyb and included updated generated files in a commit of this pull request

Motivation:

Resolves #274

Modifications:

[Describe the modifications you've done.]

Result:

[After your change, what will change.]

[Lukasa]

This change seems kinda large for the typealias: the implementation probably doesn't gain much from changing which name it uses.

[0xTim]

The theory was to make it easier for people reading code coming from platforms where they're unaware of what CryptoKit was. However, I'm easy. Closing in favour of #285