This provides a way for Nimble to natively integrate with Swift Testing. This relies on an in-progress Swift Testing Evolution proposal that I'm actively working on. You can see that PR at swiftlang/swift-testing#481.

This branch serves as a POC that the code in swiftlang/swift-testing#481 does enough to provide a way for third party assertion tools like Nimble to natively integrate with Swift Testing and report errors. As such, as my proposal evolves, this branch will change with it. Which is why this is a draft PR.

Actual Changes

• Nimble now records fileID and column information as part of the SourceLocation.
• Adds a new AssertionHandler for reporting Swift Testing errors.
• The default handler is now able to detect if a Swift Testing test is running¹, and if so, it'll report the assertion failure to Swift Testing. Otherwise, it reports the failure to XCTest.
• The new SwiftTestingAssertionHandler directly creates an Issue and uses the new-in-my-proposal Issue.record instance method.