fix(span_processor): only call on_start with recording spans

[paullegranddc]

Issue

SpanProcessor API refactor #2940

Changes

According to the spec, spans that are not recording should not be passed to span processors.
https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk.md#recording-sampled-reaction-table

This PR fixes this interaction.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.0%. Comparing base (8882c31) to head (159e336).
Report is 2 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3011   +/-   ##
=====================================
  Coverage   81.0%   81.0%           
=====================================
  Files        126     126           
  Lines      24753   24755    +2     
=====================================
+ Hits       20070   20072    +2     
  Misses      4683    4683           

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