Add starlark debugger python script interface

[quic-torgil]

This patch will add a python acript interface to the debugger together with the following tools:

• Interactive debugger
• Trace tool

See README.md for more information

[quic-torgil]

See discussion in #13387.
Demo here: https://www.youtube.com/watch?v=D7-BbD6QjeU

[hvadehra]

Looks like this could be useful to many folks, thanks for open-sourcing this!

However, it's not clear to me why this needs to be added to the Bazel codebase.

Is there any reason you'd rather not host this in a repository you own? If the worry is going out-of-sync with changes to the debugger protocol, we could consider adding this to our downstream CI. If ease-of-discovery is a concern, we could link this from the documentation somewhere.

[quic-torgil]

Is there any reason you'd rather not host this in a repository you own?

This has been starved for a while and when I saw new interest in the starlark debugger a PR was most feasible way for me right now to get it "out there" for comments and for people to reach the code. I also saw similar scripts (like ctexplain) were added to the tools section.

If the worry is going out-of-sync with changes to the debugger protocol, we could consider adding this to our downstream CI. If ease-of-discovery is a concern, we could link this from the documentation somewhere.

Awesome suggestions. Thanks. There is a number of factors talking for a separate repo also:

• Starlark debug protocol may be reused by other starlark implementations
• Support for multiple versions of Bazel (integration tests)
• Threshold to fork/improve may be lower if in a separate repo

Usually you want the "latest" version of a debugging tool even if you bisecting Bazel or using an earlier version of it.

There is a few integration issues to solve in a separate repo solution for the user experience to be as seamless as applying this patch and build the dependencies (as well as the same bandwidth issues that has delayed this to begin with).