Add InstrumentationScope and deprecate InstrumentationLibrary

[lalitb]

This spec PR open-telemetry/opentelemetry-specification#2276 introduced the concept of InstrumentationScope.

The support needs to be added without breaking the existing API for Traces. We may need to introduce another TracerProvider::GetTracer() method to add InstrumentationScope and ensure both InstrumentationLibrary and InstrumentationScope are propagated to exporters.

[lalitb]

Seems otel-proto is removing the deprecated InstrumentationLibrary from schema - https://github.com/open-telemetry/opentelemetry-proto/pull/407/files

Which means we would be able to upgrade to latest otel-proto only once this issue is fixed.