Include location of failure in XCTest test failure message

We events are enabled, we currently produce output like this:

```
> Task :xcTest FAILED

LinkedListTests.testAdd STARTED

LinkedListTests.testAdd FAILED
java.lang.Throwable: XCTAssertEqual failed: ("one") is not equal to ("two") -

LinkedListTests.testConstructor STARTED

LinkedListTests.testConstructor PASSED

2 tests completed, 1 failed
```

This tells the user that `LinkedListTests.testAdd` failed, but not where. Looking at the HTML report, I see the same message. It's only when I look at the standard error of the HTML report that I see that the assertion failed on `LinkedListTests.swift:24`. I think including this information would make things a little better without a lot of work.

Start with the events-enabled XCTest output and compare the failure message with the HTML report and its standard error, using LinkedListTests.swift:24 as the source-location example. Done means failed assertions include the source location in the displayed test failure message and the HTML report.

Written by the indexing model from the issue text.