Assertion failures aren't reported on their actual lines

[gjsjohnmurray]

We currently spot the failures in the output stream, but this lacks exact position information.

We can get this from the Location column of the %UnitTest_Result.TestAssert table, but probably only when the run has finished and we find out (from the output stream) what its RunId was.

[gjsjohnmurray]

Sketch of a solution that gives us location information during the run.

1. Add a package (e.g. VSCode.TestingManager) consisting of two classes, one extending %UnitTest.Manager and the other TestCoverage.Manager
2. Each will override LogAssert and augment the output text with location
3. Our DebugTracker's onSendMessage will use this to populate the location property of the TestMessage objects it reports.