chore!: split metrics into its own api package

[dyladan]

Create new @opentelemetry/metrics-api package

• update api readme
• update metrics api readme
• new metrics api package is a copy of the api package with non-metrics items removed
  • global utils is duplicated for now (avoids depending on api internals from metrics api)
  • global this is duplicated for now (same reason)
• remove all references to metrics from standard api package
• update imports in dependent modules
• no functionality changes of any kind
• ts references updated

Follow up:

• Move API and context-base out of lerna (new repo?)
• Shared (stable) api-common package for shared things like logging interface?
  • Currently api-metrics just depends on api to get these things.

[codecov]

Codecov Report

Merging #1797 (b165c79) into master (342b168) will increase coverage by 0.49%.
The diff coverage is 94.28%.

@@            Coverage Diff             @@
##           master    #1797      +/-   ##
==========================================
+ Coverage   92.12%   92.61%   +0.49%     
==========================================
  Files         163      174      +11     
  Lines        5484     6042     +558     
  Branches     1177     1283     +106     
==========================================
+ Hits         5052     5596     +544     
- Misses        432      446      +14     

Impacted Files	Coverage Δ
...opentelemetry-api-metrics/src/NoopMeterProvider.ts	100.00% <ø> (ø)
...ages/opentelemetry-api-metrics/src/types/Metric.ts	100.00% <ø> (ø)
packages/opentelemetry-api/src/api/global-utils.ts	100.00% <ø> (ø)
...ry-exporter-prometheus/src/PrometheusSerializer.ts	98.01% <ø> (ø)
...entelemetry-instrumentation/src/autoLoaderUtils.ts	100.00% <ø> (ø)
...es/opentelemetry-metrics/src/BaseObserverMetric.ts	100.00% <ø> (ø)
...ackages/opentelemetry-metrics/src/BatchObserver.ts	100.00% <ø> (ø)
...s/opentelemetry-metrics/src/BatchObserverResult.ts	100.00% <ø> (ø)
...ackages/opentelemetry-metrics/src/CounterMetric.ts	100.00% <ø> (ø)
...ackages/opentelemetry-metrics/src/MeterProvider.ts	89.47% <ø> (ø)
... and 32 more

[dyladan]

@open-telemetry/javascript-approvers this is extremely important for the API release so please review.

[obecny]

overall lgtm, many changes :).
Can we have a new folder "types" inside api metrics and then move there all interfaces ? Currently we have interfaces and noop Implementations together in main folder, this could help organise stuff WDYT ?

[dyladan]

@obecny made all requested changes

[obecny]

lgtm