[API EPIC 4/4] Fix tests and examples (#2587)

* Empty All of the metrics dir

* Add instrument api with documentation

* Add a NoOp implementation.

* Updated to the new config standard

* Address PR comments

* This change moves components to sdk/metrics

The Moved components are:
- metric/metrictest
- metric/number
- metric/internal/registry
- metric/sdkapi

* The SDK changes necessary to satasify the new api

* This fixes the remaing tests.

* Update changelog

* refactor the Noop meter and instruments into one package.

* Renamed pkg.Instruments to pkg.InstrumentProvider

Co-authored-by: Aaron Clawson <MadVikingGod@users.noreply.github.com>

metric/doc.go

@@ -19,49 +19,5 @@ OpenTelemetry API.
 This package is currently in a pre-GA phase. Backwards incompatible changes
 may be introduced in subsequent minor version releases as we work to track the
 evolving OpenTelemetry specification and user feedback.
-
-Measurements can be made about an operation being performed or the state of a
-system in general. These measurements can be crucial to the reliable operation
-of code and provide valuable insights about the inner workings of a system.
-
-Measurements are made using instruments provided by this package. The type of
-instrument used will depend on the type of measurement being made and of what
-part of a system is being measured.
-
-Instruments are categorized as Synchronous or Asynchronous and independently
-as Adding or Grouping. Synchronous instruments are called by the user with a
-Context. Asynchronous instruments are called by the SDK during collection.
-Adding instruments are semantically intended for capturing a sum. Grouping
-instruments are intended for capturing a distribution.
-
-Adding instruments may be monotonic, in which case they are non-decreasing
-and naturally define a rate.
-
-The synchronous instrument names are:
-
-  Counter:           adding, monotonic
-  UpDownCounter:     adding
-  Histogram:         grouping
-
-and the asynchronous instruments are:
-
-  CounterObserver:       adding, monotonic
-  UpDownCounterObserver: adding
-  GaugeObserver:         grouping
-
-All instruments are provided with support for either float64 or int64 input
-values.
-
-An instrument is created using a Meter. Additionally, a Meter is used to
-record batches of synchronous measurements or asynchronous observations. A
-Meter is obtained using a MeterProvider. A Meter, like a Tracer, is unique to
-the instrumentation it instruments and must be named and versioned when
-created with a MeterProvider with the name and version of the instrumentation
-library.
-
-Instrumentation should be designed to accept a MeterProvider from which it can
-create its own unique Meter. Alternatively, the registered global
-MeterProvider from the go.opentelemetry.io/otel package can be used as a
-default.
 */
 package metric // import "go.opentelemetry.io/otel/metric"