Proposal: incorporate superpmicollect functionality into jitutils

[BruceForstall]

The "superpmicollect" tool is both a coreclr unit test for testing SuperPMI, and a generalized SuperPMI collection harness.

Consider incorporating the superpmicollect functionality into jitutils and using it for creating a tool to easily create SuperPMI collections.

Current superpmicollect source: https://github.com/dotnet/runtime/blob/master/src/coreclr/tests/src/JIT/superpmi/superpmicollect.cs

This would somewhat duplicate the functionality in the superpmi.py script (https://github.com/dotnet/runtime/blob/master/src/coreclr/scripts/superpmi.py). However, they might be advantages in simplicity to adding it to the same suite of tools already used by the JIT, implemented in C#.

[BruceForstall]

It might be possible to then simplify the unit test to simply use the functionality in jitutils. However, that would make the coreclr test run dependent on a build of jitutils (either by doing a build or by downloading jitutils build as package), which is probably not a good dependency to create.

Alternatively, the superpmicollect unit test might be replaced with usage of superpmi.py, or might be changed to be a (close) copy of the merged source.

Or, it could be left as-is: it hasn't changed in a long time, and has not proven problematic, so we could just leave it alone.