[llvm] [llvm]Add a simple Telemetry framework (PR #102323)

[Vy Nguyen via llvm-commits]

oontvoo wrote:

> In my experience, unit test implementations are not sufficient to demonstrate how a concrete implementation works in practice, end-to-end,

Right - but what is an an end-to-end class without a concrete tool actually using Telemetry? (In this patch, no tool has  started using it yet).

The subsequent patch will have LLDB extending and using Telemetry - there you will see end-to-end the tests, of course.

So right now, the only testing meaningful for this piece of abstract library is unit tests, which, btw, are also inline with the recommendation in the [TestingGuide](https://releases.llvm.org/13.0.0/docs/TestingGuide.html#id5)  : 

>  In general unit tests are reserved for targeting the support library and other generic data structure...

https://github.com/llvm/llvm-project/pull/102323