Move the TraceFlags isSampled boolean into the SpanContext

[jkwatson]

Resolves #1603

[codecov]

Codecov Report

Merging #1628 into master will decrease coverage by 0.05%.
The diff coverage is 95.12%.

@@             Coverage Diff              @@
##             master    #1628      +/-   ##
============================================
- Coverage     86.61%   86.55%   -0.06%     
+ Complexity     1408     1397      -11     
============================================
  Files           163      163              
  Lines          5529     5497      -32     
  Branches        553      552       -1     
============================================
- Hits           4789     4758      -31     
+ Misses          544      543       -1     
  Partials        196      196              

Impacted Files	Coverage Δ	Complexity Δ
...java/io/opentelemetry/sdk/trace/data/SpanData.java	100.00% <ø> (ø)	0.00 <0.00> (ø)
...telemetry/sdk/trace/export/BatchSpanProcessor.java	90.20% <0.00%> (ø)	8.00 <1.00> (ø)
...ions/trace/jaeger/sampler/RateLimitingSampler.java	70.83% <50.00%> (ø)	7.00 <3.00> (ø)
.../main/java/io/opentelemetry/trace/SpanContext.java	90.00% <100.00%> (+2.50%)	15.00 <4.00> (+4.00)
...c/main/java/io/opentelemetry/trace/TraceFlags.java	100.00% <100.00%> (+8.10%)	6.00 <5.00> (-14.00)	⬆️
...ntelemetry/trace/propagation/HttpTraceContext.java	96.11% <100.00%> (ø)	29.00 <0.00> (ø)
...xtensions/trace/propagation/AwsXRayPropagator.java	87.20% <100.00%> (+0.15%)	26.00 <0.00> (+1.00)
...opagation/B3PropagatorInjectorMultipleHeaders.java	91.66% <100.00%> (ø)	4.00 <0.00> (ø)
.../propagation/B3PropagatorInjectorSingleHeader.java	95.65% <100.00%> (-0.35%)	5.00 <0.00> (ø)
...telemetry/extensions/trace/propagation/Common.java	72.22% <100.00%> (-2.78%)	10.00 <0.00> (ø)
... and 9 more

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[jkwatson]

@bogdandrutu @carlosalberto this is an API change. If you're interested, please review!

[carlosalberto]

Overall LGTM, thanks for this PR!

[anuraaga]

LGTM makes sense to discuss byte vs boolean separately.