Improve error messages for type mismatches

Story

Running in edr 0.9.1

- <root> = 'edr/steps'
- <docs> = GenerateDocumentation
- FileWrite <docs> '.\doc.txt'

results in this error message:

ERROR GetVariable has output type Array<Entity>, not String - (null) Line: 3, Col: 12, Idx: 70 - Line: 3, Col: 17, Idx: 75 Text: <docs>

It would be much clearer if the error message is:

ERROR FileWrite expected a String for parameter Text, but <docs> is an Array<Entity>.