[PoC] Reimplement OpenCensus bridge

[dashpole]

Fixes https://github.com/open-telemetry/opentelemetry-go/issues/2808

The first three commits are:

• https://github.com/open-telemetry/opentelemetry-go/pull/3098
• https://github.com/open-telemetry/opentelemetry-go/pull/3099
• https://github.com/open-telemetry/opentelemetry-go/pull/3100

The final commit is the implementation of the OpenCensus bridge.

It follows the design described in https://github.com/open-telemetry/opentelemetry-specification/pull/2722, and https://github.com/open-telemetry/opentelemetry-specification/pull/2732.

[codecov[bot]]

Codecov Report

Merging #3093 (70185b3) into main (d7bfe66) will decrease coverage by 0.0%. The diff coverage is 58.1%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3093     +/-   ##
=======================================
- Coverage   77.3%   77.2%   -0.1%     
=======================================
  Files        159     160      +1     
  Lines      11139   11178     +39     
=======================================
+ Hits        8613    8638     +25     
- Misses      2329    2342     +13     
- Partials     197     198      +1     

Impacted Files	Coverage Δ
sdk/metric/config.go	91.0% <16.6%> (-9.0%)	:arrow_down:
sdk/metric/pipeline.go	91.0% <27.7%> (-6.3%)	:arrow_down:
bridge/opencensus/metric.go	45.1% <100.0%> (+45.1%)	:arrow_up:
bridge/opencensus/version.go	100.0% <100.0%> (ø)
sdk/metric/provider.go	100.0% <100.0%> (ø)
exporters/jaeger/jaeger.go	91.1% <0.0%> (+0.8%)	:arrow_up:
sdk/trace/batch_span_processor.go	81.9% <0.0%> (+0.8%)	:arrow_up:

[dashpole]

This is now rebased on main (from the new_sdk/main branch)