fix(sdk-metrics-base): remove aggregator.toMetricData dependency on AggregationTemporality

[legendecas]

Which problem is this PR solving?

The aggregator interface may be implemented by users in the future extension. This PR simplifies the API surface of Aggregator.toMetricData to make it an opaque transformation from aggregator-specific Accumulation to exported MetricData. As aggregators do not need to process AggregationTemporality (they only need to expose merge and diff for metric processors to handle them), this should also apply to toMetricData.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• Unit tests have been updated

[codecov]

Codecov Report

Merging #2676 (49ac14f) into main (6b94e26) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 49ac14f differs from pull request most recent head e35d992. Consider uploading reports for the commit e35d992 to get more accurate results

@@            Coverage Diff             @@
##             main    #2676      +/-   ##
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- Coverage   93.03%   93.03%   -0.01%     
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  Files         155      155              
  Lines        5373     5368       -5     
  Branches     1133     1131       -2     
==========================================
- Hits         4999     4994       -5     
  Misses        374      374              

Impacted Files	Coverage Δ
...metry-sdk-metrics-base/src/aggregator/Histogram.ts	97.91% <0.00%> (-0.09%)	⬇️
...entelemetry-sdk-metrics-base/src/aggregator/Sum.ts	100.00% <0.00%> (ø)
...ntelemetry-sdk-metrics-base/src/aggregator/Drop.ts	100.00% <0.00%> (ø)
...telemetry-sdk-metrics-base/src/aggregator/types.ts	100.00% <0.00%> (ø)
...metry-sdk-metrics-base/src/aggregator/LastValue.ts	100.00% <0.00%> (ø)
...-metrics-base/src/state/TemporalMetricProcessor.ts	97.91% <0.00%> (+0.04%)	⬆️