Move span exporter module

[cijothomas]

#2534, applied to Span.

opentelemetry_sdk::export::spans::{ExportResult, SpanData, SpanExporter};
to
opentelemetry_sdk::logs::{ExportResult, SpanData, SpanExporter};

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 77.8%. Comparing base (a0e5061) to head (2d3d093).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-stdout/src/trace/exporter.rs	0.0%	2 Missing ⚠️
opentelemetry-otlp/src/span.rs	0.0%	1 Missing ⚠️
opentelemetry-sdk/src/trace/runtime_tests.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2540   +/-   ##
=====================================
  Coverage   77.7%   77.8%           
=====================================
  Files        123     123           
  Lines      23050   23047    -3     
=====================================
  Hits       17931   17931           
+ Misses      5119    5116    -3     

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