Fix slicing cardinality validation

[ngfreiter]

This makes it so that if a single element is sliced, we allow it as long as it is inherited from a parent element. But if the FSH tries to apply a contains rule on a single element, we log an error.

For example, this should be an error:

Profile: V
Parent: Immunization
* vaccineCode ^slicing.discriminator.type = #pattern
* vaccineCode ^slicing.discriminator.path = "$this"
* vaccineCode ^slicing.rules = #open
* vaccineCode ^slicing.description = "Slicing example"
* vaccineCode contains slice1 0..1 and slice2 0..1

But if you test the similar situation in the https://github.com/hl7ch/ch-etoc IG on the ChEtocImmunizationSection, which inherits from the ChVacdImmunizationSection profile, it should log no error, because the slicing is introduced in a dependency, not in the FSH itself.

[cmoesel]

This works well. I only have a couple of minor suggestions regarding the error itself.

[cmoesel]

Looks good! @mint-thompson or @julianxcarter -- can we get a second review on this by mid-afternoon-ish?

[julianxcarter]

Works well!