Improve ExprXOf Literal Handling

[APickledWalrus]

Problem

ExprXOf no longer allowed seemingly non-literal inputs (e.g. arithmetic) due to a check it has to prevent literal inputs. This is so that syntax like 10 of diamond instead parses using the itemtype literal parser.

Solution

The solution is to check the source of the literal. If the source of the literal is another literal, it was likely created by the parser (and not from a simplified syntax). The source of parser-created literals will always be a literal. Additionally, I cleaned up the class and corrected a mistake with the return types implementation. It is not correct to simply mirror the possible return types of the source Expression. For example, if the possible return types were ItemStack and Integer (whereas this expression would only return an ItemStack).

Testing Completed

I added a test for a statement that previously failed to parse.

Supporting Information

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Completes: none
Related: #8080