Add BaseScopeManager interface

[vmarchaud]

Based on #65

I mostly based the API on the Opencensus one, i will explain the choice i made for each function so we have a starting point for the discussion.

[mayurkale22]

@vmarchaud #65 has been merged, please rebase with the master.

[vmarchaud]

I've changed the interface based on all feedbacks @mayurkale22 @rochdev @draffensperger

[vmarchaud]

Addressed comments by @rochdev. I've also renamed the packages to scope-base following comment by @rochdev saying that Context was already heavily used across the implementation so using scope will be clearer.

[codecov-io]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.03%. Comparing base (14310c3) to head (af3e99f).

Additional details and impacted files

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##           master      #66   +/-   ##
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  Coverage   98.03%   98.03%           
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  Files          13       13           
  Lines         204      204           
  Branches        8        8           
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  Hits          200      200           
  Misses          4        4           

[draffensperger]

Given that this is just an interface for now, would it make sense to have it in @opentelemetry/types? What's the motivation for a separate package for the base scope?

I like the idea of having the actual implementations be in their own packages, but not sure the interface needs its own. @rochdev WDYT?

[vmarchaud]

@draffensperger I believe the goal was the package to be usable outside of opentelemetry, so having the interface in core would mean add another dependency.

[rochdev]

LGTM

@mayurkale22 @danielkhan is it fine to use Scope instead of Context from the spec perspective?

[mayurkale22]

@mayurkale22 @danielkhan is it fine to use Scope instead of Context from the spec perspective?

I think it is fine to use Scope, looks like Java and .NET uses the same terminology https://github.com/open-telemetry/opentelemetry-java/blob/master/api/src/main/java/io/opentelemetry/context/Scope.java

[vmarchaud]

Addressed comments once again, i believe it's good to land now.
(@rochdev could you remove the requested changes ? i think it will block the PR otherwise)

[rochdev]

I would rename the first parameter of bind to target since it may not be an object but otherwise LGTM.

[mayurkale22]

I would rename the first parameter of bind to target since it may not be an object but otherwise LGTM.

@vmarchaud Feel free to handle it in separate PR, merging it now. Thanks for the work and PR!