With Swift 6.1 the extractor will start to extract files outside of the test
directory. These files and their elements we do not want to see in our tests.
The test was inspired by locally running the query against files in
https://github.com/apple/swift/tree/main/test/Parse
A query for missing elements was also added to the AST tests, expecting
nothing to be found.
As `ASTMangler` crashes when called on `ModuleDecl`, we simply use
its name.
This might probably not work reliably in a scenario where multiple
modules are compiled with the same name (like `main`), but this is left
for future work. At the moment this cannot create DB inconsistencies.
