Check that semconv referenced in `renamed_to` exists

[lmolkova]

Let's say I write

  - id: code.filepath
    stability: development
    ....
    deprecated:
      reason: renamed
      renamed_to: does.not.exist # this one does not exist

I don't get any error from the weaver, so I added a semconv policy into open-telemetry/semantic-conventions#2047, which checks that:

1. there is an attribute (metric/event/etc depending on what's deprecated) with this identity
2. it's not deprecated

p2 is probably a preference and belongs in the semconv policy, but the p1 seems to belong in the weaver resolution process. We should try resolving it similarly to ref or extends and fail if it's not found.

So I think we should have p1 is weaver