DSLX interpreter should have a trace mode for proc state

forked from #824

It'd be good to have a mode in the interpreter where the proc state is dumped to stderr at the beginning of a tick. It could be enabled with a flag like so:

```
bazel run foo_test -- --trace_procs
```

Would also would be good to have a regexp filter for which procs to trace like so

```
bazel run foo_test -- --trace_procs --trace_procs_filter=.*Foo.*
```