Add a new module reachability which implements the reachability algorithm. Add the end to end logic for the reachability starting from all the harnesses in the target crate.

## Resolved issues:

Resolves #1672

## Related RFC:

#1588

## Call-outs:

    We still need to build the custom sysroot in order to fix the missing functions issue.
    I added a mechanism to run the regression tests using the MIR linker inside compiletest.
    I ran the regression manually (with the mir_linker enabled) the only tests that didn't pass were:
        cargo-kani/asm/global_error/doesnt_call_crate_with_global_asm.expected: The global assembly is out of the scope so it doesn't get processed. If we want to keep that behavior, we will have to inspect all items manually.
        cargo-kani/cargo-tests-dir/expected: This might be a legit issue that I need to fix on kani-driver logic.
        cargo-ui/dry-run/expected: Not an issue (arguments to the compiler changes).