Ensure ExpressionList#possibleReturnTypes is accurate after getConvertedExpression

[sovdeeth]

Problem

During the implementation of type properties, I had some issues with determining the possible return types of a converted ExpressionList. If I converted me and {tool} to Player and ItemType, it would give me a EL with the possibleReturnTypes of Player and Object. In getConvertedExpression, it was taking getReturnType of the component expressions and using that for possible return types, rather than asking for possibleReturnTypes to get the most accurate information.

Solution

The solution was to add all the possibleReturnTypes from the elements into a set and use that as the list's possible return types. This avoids unnecessary supertypes and gives the most accurate information.

Testing Completed

Manual confirmation. This will be tested further once type properties is implemented.

Supporting Information

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Completes: none
Related: none