MaxLength should succeed when run on non-strings

[mmsmits]

Identical to what we do with BindingAssertion on a non-bindeable element.

[mmsmits]

Moved from: https://firely.atlassian.net/browse/VONK-4005

[mmsmits]

If users use a MaxLength on a non-string we fail.

On the compiler side we should report if there is a MaxLength on a string.
However, on choice types, we can't always know and should just ignore non-strings (or other non-compatible types) when checking MaxLength.

[mmsmits]

Please take a look at https://www.hl7.org/fhir/elementdefinition-definitions.html#ElementDefinition.maxLength to determine whether this is relevant and/or needs its own issue.