Remove "(unknown context at $xxxxxxxx)" from fully-qualified type names. (#525)

This PR ensures that the aforementioned gunk doesn't show up in our
string representations of suites and type IDs. These substrings indicate
that a type is `private`, nested in a function, or otherwise might have
a non-unique Swift name. We don't care: Swift Testing will treat two
private types with the same (otherwise qualified) name in the same
module as the same type and will ultimately disambiguate tests in them
by source location if needed.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/Parameterization/TypeInfo.swift

@@ -104,6 +104,11 @@ extension TypeInfo {
         result[0] = String(firstComponent.split(separator: ":", maxSplits: 1).last!)
       }
 
+      // If a type is private or embedded in a function, its fully qualified
+      // name may include "(unknown context at $xxxxxxxx)" as a component. Strip
+      // those out as they're uninteresting to us.
+      result = result.filter { !$0.starts(with: "(unknown context at") }
+
       return result
     case let .nameOnly(fullyQualifiedNameComponents, _, _):
       return fullyQualifiedNameComponents