Try varying interactive draws in `Phase.explain`

[Liam-DeVoe]

Phase.explain currently only tries to vary the known-ahead-of-time args and kwargs to the test function, via arg_slices. This does not include interactive draws from st.data() - so, we should fix that!

• Run explain-phase experiments on interactive draws as well, possibly by simply adding their choice sequence ranges to arg_slices.
• Add comment annotations to the printed Draw 1: ... output from the experiment results, like we do for function arguments. slice_comments.
  • Probably by adding to slice_comments (as for function arguments), and handling interactive-draw slices specially when printing dynamic draws?

(via #4399 (comment))

[Zac-HD]

I'd also love to revive #3624 now that everything is IR-based!