Bloaty should have -d source:provider modifiers

When debugging data quality issues with Bloaty, we frequently want to answer the question "how did a given byte get attributed?" If Bloaty's results are implausible or buggy, we want to know what went wrong, and localize that to one part of the code.

In the code, every time we add a range to a `RangeSink`, we give a parameter `analyzer` which is just a static label in the code, for example: `elf_sections`, `dwarf_pcpair`, etc.

It would help with debugging if a map (as viewable with `--raw-map`) could show the provider that attributed a given range. Then you could debug with something like:

```
$ bloaty -d compileunits,compileunits:provider --raw-map
```

This could help debug issues like https://github.com/google/bloaty/issues/176 more easily, especially if it's not easy to supply a repro.