Don't do type checking when linking a ModeTransitionTrigger's context.
Link any visible Context and let the validator do the type checking.
Don't do type checking when linking a ModeTransitionTrigger's
triggerPort.  Link any visible TriggerPort and let the validator do the
type checking.
Type check the context and triggerPort of a ModeTransitionTrigger in the
validator instead of the linker.
Created a validation test for the type checking of a
ModeTransitionTrigger.