Add a source line resolver for tests

[enlight]

Currently tests that need to check that the debugger ends up at the right source line rely on hard-coded line numbers, this is rather tedious to maintain and easy to break whenever modifying the source of the test targets. A better way to accomplish this sort of thing is to place some marker comments in the target source file and then look for them when running tests to determine the corresponding line number.

[enlight]

A source line resolver was added in dfb9f74
Now need to update the tests to use it.