Summary:
This adds support for vscode. The C++ extension and LLDB extension need to be installed.

run
`python scripts/generate_vscode_tasks.py` to do the setup. After this you can just run the task from within vscode.

To use the lldb debugger you need a patched version:
`https://github.com/pixie-labs/vscode-lldb`

Otherwise, you can just use the builtin cpp debugger but it's not as good.

You need to add `build --spawn_strategy=standalone`  to `.bazelrc` to get this to work. It's non-ideal but we need it until: https://github.com/bazelbuild/bazel/issues/6327 is fixed.

Test Plan: Tested on vscode 1.30.1/

Reviewers: #engineering, kgandhi

Reviewed By: #engineering, kgandhi

Differential Revision: https://phab.corp.pixielabs.ai/D171

GitOrigin-RevId: a8fee13b649cfd8d9a3df7d18572b02140e3dbac