Update TraceIdRatioBasedSampler to calculate sampling threshold according to OTEP 235

[Nevay]

Computes the sampling threshold as defined in open-telemetry/opentelemetry-specification#4166.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.56%. Comparing base (20bf3cf) to head (96bebeb).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1391      +/-   ##
============================================
- Coverage     73.56%   73.56%   -0.01%     
- Complexity     2672     2679       +7     
============================================
  Files           386      386              
  Lines          7650     7659       +9     
============================================
+ Hits           5628     5634       +6     
- Misses         2022     2025       +3     

Flag	Coverage Δ
8.4	73.56% <100.00%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
src/SDK/Trace/Sampler/TraceIdRatioBasedSampler.php	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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