Starting debugger should re-run starlark code

If you start debugging a target that you've built before, no breakpoints are hit. I guess right now you just have to manually `bazel shutdown` every time you start debugging? It seems like the debugger should do this automatically at the start of a debug session as I don't see the use in starting a debug session that is guaranteed to not hit any breakpoints.

Trace the VS Code debugger start flow and the Bazel shutdown behavior described in the issue. Reproduce the case with a previously built target and a breakpoint, then verify that starting a debug session reruns the relevant Starlark code and reaches the breakpoint without requiring manual bazel shutdown.

Written by the indexing model from the issue text.