Integrity check for data processor plugins

Problem: data processor plugins such as the TokenProcessor need to take part in the integrity check process. They might need to validate if all the variables they are using from the execution metadata state are valid or if they can even be applied to a context of a certain type. Example: it does not make sense to have a token processor on a enttity:node context. Token replacements are only possible on strings.

Proposed solution: add a checkIntegrity() method to the data processor interface which gets an ExecutionMetadataStateInterface + the ContextDefinition + context name that is being checked for integrity.

The invocation of that can method con be done in IntegrityCheckTrait.

Add test cases that verify only valid tokens are used with the token processor.