Aggregation Temporality Support

[legendecas]

Which problem is this PR solving?

• Refs: [Metrics] Metrics SDK export pipeline tracking issue #1528
• Add stateless accumulations support.

Short description of the changes

• Make metrics and bound metrics state ephemera, so that a label set will not be kept in store throughout the process lifetime without manual unbind.
• Rename UngroupedProcessor to BasicProcessor and supports cumulative processing to aggregate AggregationTemporality.DELTA aggregator snapshots to AggregationTemporality.CUMULATIVE accumulations.
• Add move and merge to Aggregator interfaces.

This PR depends on previous minor type introductions:

• feat: processor export phases interface #1717
• feat: introduce AggregatorSelector type #1712

[legendecas]

As the aggregator in the Accumulator (class Metric in the context) no longer bookkeeping all the records of past label-aggregator pairs, it is impractical for SumObserver to determine if it is updating with a rising value (unless the observer itself memos last value, but I'm not favoring the workaround). Some practices may recognize the value drop as a reset and correctly reflect the true trend, So I'd believe the value drop in SumObserver can reflect the true trends rather than discarding data frames.

[obecny]

SumObserver cannot have value drop, this is monotonic metric - it can only raise or remain the same.

[legendecas]

Yeah, you are right. I've checked again the status quo PR of the processor specs, SumObserver and
UpDownSumObserver instruments are configured for Cumulative aggregation temporality in StatelessAggregationTemporalitySelector .

[codecov]

Codecov Report

Merging #1730 (fa3617c) into master (781b30f) will decrease coverage by 0.46%.
The diff coverage is 80.54%.

@@            Coverage Diff             @@
##           master    #1730      +/-   ##
==========================================
- Coverage   91.38%   90.91%   -0.47%     
==========================================
  Files         164      165       +1     
  Lines        5059     5153      +94     
  Branches     1048     1070      +22     
==========================================
+ Hits         4623     4685      +62     
- Misses        436      468      +32     

Impacted Files	Coverage Δ
...ages/opentelemetry-metrics/src/export/Processor.ts	100.00% <ø> (+8.00%)	⬆️
...emetry-metrics/src/export/aggregators/Histogram.ts	76.19% <47.36%> (-23.81%)	⬇️
...s/opentelemetry-metrics/src/BatchObserverMetric.ts	92.85% <50.00%> (-0.25%)	⬇️
packages/opentelemetry-metrics/src/Utils.ts	68.75% <59.09%> (-21.25%)	⬇️
...emetry-metrics/src/export/aggregators/LastValue.ts	79.16% <61.53%> (-20.84%)	⬇️
...opentelemetry-metrics/src/export/BasicProcessor.ts	80.55% <80.55%> (ø)
...kages/opentelemetry-metrics/src/BoundInstrument.ts	94.73% <87.50%> (-5.27%)	⬇️
...ges/opentelemetry-metrics/src/export/Controller.ts	80.76% <88.88%> (+1.60%)	⬆️
...pentelemetry-metrics/src/export/aggregators/Sum.ts	95.83% <92.30%> (-4.17%)	⬇️
...es/opentelemetry-metrics/src/BaseObserverMetric.ts	100.00% <100.00%> (ø)
... and 10 more

[legendecas]

Closed due to inactivity. I will continue the investigation once there are any updates on the spec.