Performance variable and APIs

[wrrobin]

An initial draft of the OpenSHMEM performance variables and corresponding APIs is attached:
PVAR_APIs_Spec_F2F_09_26_19.pptx

Opening this issue to identify and gather all the feedback related to the initial proposal.

[davideberius]

OpenSHMEM Tools Information Interface (shmem_t).pdf

SHMEM Tools Interface presentation from May 18th 2023 Working Group Meeting.