TGG Editor: Validation and handling of EDatatypes in attribute conditions

[anthonyanjorin]

A validation should be used to ensure that attribute conditions really make sense (regarding types). E.g. eq_string(bla.blup, "Foo") should ensure that both values are really of type EString...

A related problem is that the method csp.RuntimeTGGAttributeConstraintContainer.coerceToType assumes that all data types have an instance class. This is only the case for standard EDatatypes already defined in Ecore, or for EDataTypes for which the user supplies and registers generated code. For all other cases this returns null, and we should throw an exception telling the user that a user-defined attribute condition is required for this.

[anthonyanjorin]

Also things like eq_string(f.baz, 234523) for cases where f.baz is a string are not validated. I just tried it out and some weird number (not 234523) is fixed as string value.