Make TypeFactory injectable

[Chris Müller]

The TypeFactory has a static method createType() by now, which [creates the correct type model class. It was introduced to ease the creation of types independent from the namespace of that class and to avoid adjustments when a type is moved from pending to core section. But this approach has some drawbacks:

• It is hard to test the classes which use this factory (for example, when using fixture types)
• The factory cannot be overridden/injected (which is useful in some cases).
• As the factory is not instantiated, dependencies (which may be needed some day) cannot be injected.

For these reasons the TypeFactory is adjusted:

• The TypeFactory must be injected via DI. (This way the constructor arguments are not part of the API.)
• It implements a non-static method create() which returns the given type (like the old createType static method).
• The createType() method is marked as deprecated and triggers a deprecation notice on usage.
• The examples in the documentation are adjusted.
• The createType() method is listed in the deprecation chapter and will likely be removed in version 4.0.0.
• A deprecation entry in the changelog is added.

This was inspired by a discussion in TYPO3 Slack.