prevent attempt to create method that will fail for missing return type

[homberghp]

closes #8594

Implementation: Add method to test that the return type given is useable by the CreateMethod fix.

Uses that method in 4 places in CreateElement.

Added test to verify that no fix is suggested by create element. Added test data file with minimal working example as given in #8594

With this fix in place, the hint to create a method is not shown; instead, the line with the combination of var type and unknown method call is flagged as an error.

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