* Store Span instead of local/remote SpanContext in Context
Now that the SpanContext has a remote identifier, storing a Span's
SpanContext two separate ways in a Context (one for local another for
remote) is unnecessary and adds complication throughout the project when
determining heredity of a Span. This moves to storing the Span directly
in the Context uniformly (for both local and remote) as current Span. In
the process, it updates the getter/setter functionality the `trace`
package provides and replaces the distributed heredity logic throughout
the project with just using the current Span as the parent if it exists.
* Update trace/context.go
Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>
* Assert propagators context remote state
Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>
