Split package in two, to separate building profile protos from visualizing profiles

[NHDaly]

Problem

• pprof_jll now depends on Graphviz_jll since add Graphviz as dependency to PProf JuliaPackaging/Yggdrasil#5652.
• this is an attempt to address Ship graphviz? #16
• This has some disadvantages
  • dependency bloat
  • adding packages with licenses some users may not want (e.g. custom libpng license, LGPL license for Cairo)
• It’s a significant number of JLLs that are added.
  • graphviz, pango, cairo, etc.

Proposal

Some users don't actually need pprof_jll as a dependency (for example, at RAI). The parts of PProf.jl that we do need, are the parts that convert a profile into the pprof protobuf format. The pprof_jll is there for users to be able to visualize the profiles. We only use PProf for generating protos, as part of https://github.com/JuliaPerf/PerformanceProfilingHttpEndpoints.jl.

What this suggests to me is that probably we should split the PProf package in two (in the same repo):

• PProf.jl (Visualization + generating profiles), and
• PProfProducer, or PProfConverter, or PProfCore, or something like that, which is a package that just provides the profile => pprof.pb.gz conversion functionality.

Then RAI could depend only on the latter, and thus we wouldn't depend on graphviz_jll.

[NHDaly]

@quinnj for triage :)