Type Parameters are not checked

[adamretter]

eXist-db does not appear to correctly support and enforce type parameters, e.g. map(xs:integer, xs:string) and element(my-name).

As such the eXist XQTS Test Runner takes a relaxed approach to checking them, see: https://github.com/eXist-db/exist-xqts-runner/blob/master/src/main/scala/org/exist/xqts/runner/TestCaseRunnerActor.scala#L1042.
This means that at present we may report passes where we should report failures. We have two options:

1. Fix eXist-db and implement the strict checks in the XQTS Test Runner, with the aim of passing the tests.
2. Don't for eXist-db and implement the strict checks in the XQTS Test Runner, which will show further XQTS test failures.

[line-o]

Strongly in favour of option 2.
A first PR to check for function types is already open eXist-db/exist#3389