Port Create a new entity (entity_create) action to D8

This needs a check to ensure the entity can be added through the UI. Entities like contact form messages and payments shouldn't just be added anywhere. IIRC Rules for Drupal 7 uses a simple boolean flag in the entity type definition. Maybe we can do the same here?

My current progress is up at https://github.com/fago/rules/pull/146

I was unable to complete this because of issues with the test framework, as discussed with fago.

We also decided to skip the check in #1, if an entity type is able to be constructed using entity_create(), then the same reasons apply to this action. Modules with corner cases can alter the definition and unset the derivative for the entity type they want to hide.

Thanks, I commented the PR - functionality basically looks great. So it's "just" missing tests then.

I am writing the tests for this @drupaldevdays Montpellier.

The pull request is at https://github.com/fago/rules/pull/158

Merged, thanks!