fix(monitoring-exporter): convert to GCM format based on metric data type, not instrument type

[aabmass]

This makes the exporter work with views (see included snapshot test), where the data point type will not match the instrument type. Otherwise the behavior of the exporter is unchanged.

Note the InstrumentDescriptor.name is still the only place to get the metric's name and it actually will match the name configured for output in the view. This is confusing, discussion going on in open-telemetry/opentelemetry-js#3439

[codecov]

Codecov Report

Merging #453 (b347659) into main (375e1be) will decrease coverage by 0.06%.
The diff coverage is 72.22%.

❗ Current head b347659 differs from pull request most recent head c96c019. Consider uploading reports for the commit c96c019 to get more accurate results

@@            Coverage Diff             @@
##             main     #453      +/-   ##
==========================================
- Coverage   92.74%   92.68%   -0.07%     
==========================================
  Files          13       13              
  Lines         441      451      +10     
  Branches       85       86       +1     
==========================================
+ Hits          409      418       +9     
- Misses         32       33       +1     

Impacted Files	Coverage Δ
...emetry-cloud-monitoring-exporter/src/monitoring.ts	88.04% <70.58%> (+2.65%)	⬆️
...lemetry-cloud-monitoring-exporter/src/transform.ts	80.00% <73.68%> (-2.06%)	⬇️

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