Exemplars are broken for long histograms

[jack-berg]

If you try to record to LongHistogram in the context of a sampled span, an exemplar will not be included on collection. However, DoubleHistogram works as expected. I looked into it and its due to HistogramPointData only returning double histogram. Under the covers, we record the value as a long to the ReservoirCell, and then try to read out the cell's doubleValue, which doesn't exist.

From @dashpole:

Using the logging exporter, I can confirm that it isn't an issue with the prometheus exporter:

INFO: metric: ImmutableMetricData{resource=Resource{schemaUrl=null, attributes={service.name="PrometheusExporterExample", telemetry.sdk.language="java", telemetry.sdk.name="opentelemetry", telemetry.sdk.version="1.22.0"}}, instrumentationScopeInfo=InstrumentationScopeInfo{name=io.opentelemetry.example.prometheus, version=null, schemaUrl=null, attributes={}}, name=super.timer, description=, unit=ms, type=HISTOGRAM, data=ImmutableHistogramData{aggregationTemporality=CUMULATIVE, points=[ImmutableHistogramPointData{getStartEpochNanos=1676326373284000000, getEpochNanos=1676326433302000000, getAttributes={}, getSum=59053.0, getCount=59, hasMin=true, getMin=1000.0, hasMax=true, getMax=1026.0, getBoundaries=[0.0, 5.0, 10.0, 25.0, 50.0, 75.0, 100.0, 250.0, 500.0, 750.0, 1000.0, 2500.0, 5000.0, 7500.0, 10000.0], getCounts=[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 31, 28, 0, 0, 0, 0], getExemplars=[ImmutableDoubleExemplarData{filteredAttributes={}, epochNanos=1676326429485000000, spanContext=ImmutableSpanContext{traceId=ef29eebb7cde692aa527d9c114b384af, spanId=e0a4334cc4242518, traceFlags=01, traceState=ArrayBasedTraceState{entries=[]}, remote=false, valid=true}, value=0.0}, ImmutableDoubleExemplarData{filteredAttributes={}, epochNanos=1676326432488000000, spanContext=ImmutableSpanContext{traceId=9c16ce50f3788156dc0fb8424810b7bb, spanId=94e329af9852cc7c, traceFlags=01, traceState=ArrayBasedTraceState{entries=[]}, remote=false, valid=true}, value=0.0}]}]}}

The values of both are 0.0, even though only higher buckets have any observations.

Originally posted by @dashpole in open-telemetry/opentelemetry-java-examples#96 (comment)

[jack-berg]

Resolved by #5216