use new api function from_remote_span for propagated span context

[tsloughter]

Thanks to @dvic for catching this issue. Long story of how it happened but put simply it is both the result of spec churn (how remote spans were defined/stored changed multiple times) and relying on unit tests.

Note that the unit test issue is not fixed in this PR, so a follow up is needed with additional integration tests that propagate a span context and then runs the remote/local parent based samplers after extracting.

I had only been testing the sampler against span contexts defined in the tests instead of ones created by propagation, this meant is_remote was set properly in the test span_ctx even though it wouldn't be in actual usage when a span came through the propagator.

[codecov]

Codecov Report

Merging #265 (a845aa6) into main (edfd222) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #265      +/-   ##
==========================================
+ Coverage   36.39%   36.41%   +0.02%     
==========================================
  Files          37       37              
  Lines        3165     3166       +1     
==========================================
+ Hits         1152     1153       +1     
  Misses       2013     2013              

Flag	Coverage Δ
api	62.90% <100.00%> (-0.14%)	⬇️
elixir	16.05% <0.00%> (-0.04%)	⬇️
erlang	36.41% <100.00%> (+0.02%)	⬆️
exporter	19.58% <ø> (ø)
sdk	79.10% <ø> (+0.17%)	⬆️

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Impacted Files	Coverage Δ
.../opentelemetry_api/src/otel_propagator_http_b3.erl	64.51% <100.00%> (ø)
...opentelemetry_api/src/otel_propagator_http_w3c.erl	50.90% <100.00%> (ø)
apps/opentelemetry_api/src/otel_tracer.erl	59.25% <100.00%> (-2.28%)	⬇️
apps/opentelemetry/src/otel_resource_detector.erl	92.85% <0.00%> (+1.42%)	⬆️

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