Re-add previous metric bridge

[dashpole]

I realized its ~trivial to support the previous method of invoking the OC metric bridge, so it might be best to include this, rather than break users until the new design is ready. See https://github.com/open-telemetry/opentelemetry-go/pull/3184#issuecomment-1251199036

Opening this as an option.

[codecov[bot]]

Codecov Report

Merging #3192 (84fbef7) into main (b6d4335) will decrease coverage by 0.1%. The diff coverage is 0.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3192     +/-   ##
=======================================
- Coverage   77.4%   77.3%   -0.2%     
=======================================
  Files        158     159      +1     
  Lines      11084   11101     +17     
=======================================
  Hits        8583    8583             
- Misses      2306    2323     +17     
  Partials     195     195             

Impacted Files	Coverage Δ
bridge/opencensus/internal/ocmetric/metric.go	93.8% <ø> (ø)
bridge/opencensus/metric.go	0.0% <0.0%> (ø)

[MrAlias]

Depends on fix in https://github.com/open-telemetry/opentelemetry-go/pull/3193

[dashpole]

I had to move the opencensusmetric/internal package because it wasn't accessible from where I wanted to place the bridge...

[dashpole]

rebased on the test fix