[Parent issue]: SpanProcessor API refactor

[paullegranddc]

Parent issue for SpanProcessor API related issues

[paullegranddc]

@cijothomas I don't think I have the permissions to link sub-issues, but here are the ones I think make sense:

• Tracing SDK - Processors get clone of SpanData which is incorrect
• [Feature]: Reading spans through the public API requires cloning everything to SpanData