FormatTest: Provide real line number in failure messages

Currently a test failure always reports a line number inside verifyFormat()
which is not very helpful to see which test failed. With this change we now
emit the line number where the verify function was called. When using an
IDE such as CLion, the output now includes a clickable link that points to
the call site.

Reviewed By: MyDeveloperDay

Differential Revision: https://reviews.llvm.org/D86926