rust/src/tools/coverage-dump

This tool extracts coverage mapping information from an LLVM IR assembly file (.ll), and prints it in a more human-readable form that can be used for snapshot tests.

The output format is mostly arbitrary, so it's OK to change the output as long as any affected tests are also re-blessed. However, the output should be consistent across different executions on different platforms, so avoid printing any information that is platform-specific or non-deterministic.