Record SourceContext in InstrumentationScope.Name

[nblumhardt]

See: open-telemetry/opentelemetry-dotnet#4941

This should probably remove SourceContext from the regular set of attributes.

I'm uncertain whether all receivers will provide a pleasant consumption experience for instrumentation scope names, we might consider gating the new behavior on a (default-enabled) IncludedData.InstrumentationScopeName or similar, in the 1.x series of releases, so that the setting can be disabled and the old behavior restored if needed.