R4 FHIRPathEngine resolveConstant of EvaluationContext doesn't support returning multiple values

[shoaibmushtaq25]

In the context of a conversation with @grahamegrieve over zulip chat,

R4 FHIRPathEngine public Base resolveConstant(Object appContext, String name, boolean beforeContext) method of EvaluationContext Interface doesn't support returning multiple values.

cc: @grahamegrieve

[grahamegrieve]

This is already done in the R5 version

[grahamegrieve]

This is already done in R5 - just have to copy the same code across