Use "profiles" and "scenarios" terminology consistently.

[nnethercote]

Specifically:

• Rename the --builds and --runs options as --profiles and
  --scenarios, respectively. The old option names are still available
  as aliases, for backward compatibility.
• Replace the use of "profile kinds" and "scenario kinds" (and
  variations) with just "profiles" and "scenarios". Note that this
  required renaming the PerfTool::Profile variant as
  PerfTool::ProfileTool to avoid a collision with the new Profile
  type.
• Fix various inconsistencies in the docs.

[rylev]

Thanks! I've been meaning to do this for a while! Have you run things locally and tried to make sure nothing has broken?

[nnethercote]

I have done some local testing of bench_local, profile_local, and loading the "compare" page on the site. Plus the CI actions passed, which test a bunch of things. It's possible that some breakage will fall through the gaps, though.

[Mark-Simulacrum]

I'll go ahead and merge, and if there's any fall out we can fix that up. I think this looks pretty good though.

[nnethercote]

One nice thing about this change is that "runs" was being used in two ways: in some places it meant what we now call "scenarios", and in other places it refers to how many times a benchmark is run. Only the latter meaning now remains.