Support a global MeterProvider in go.opentelemetry.io/otel (#3818)

* Move ErrorHandler impl to internal

To avoid the import cycle, the otel/metric package needs to not import
otel. To achieve this, the error handling implementation is moved to the
otel/internal/global package where both can import the needed
functionality.

* Add global metric to go.opentelemetry.io/otel

* Crosslink and update to global metric in otel

* Add changes to changelog

* Set PR number in changelog

* Add global metric unit tests

* Rename MeterProivder() to GetMeterProivder()

* Add TODO to remove nolint comments

metric.go

@@ -0,0 +1,61 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package otel // import "go.opentelemetry.io/otel"
+
+import (
+	"go.opentelemetry.io/otel/metric"
+	// TODO (#3819): Remove this disablement.
+	// nolint: staticcheck  // Temporary, while metric/global is deprecated.
+	"go.opentelemetry.io/otel/metric/global"
+)
+
+// Meter returns a Meter from the global MeterProvider. The name must be the
+// name of the library providing instrumentation. This name may be the same as
+// the instrumented code only if that code provides built-in instrumentation.
+// If the name is empty, then a implementation defined default name will be
+// used instead.
+//
+// If this is called before a global MeterProvider is registered the returned
+// Meter will be a No-op implementation of a Meter. When a global MeterProvider
+// is registered for the first time, the returned Meter, and all the
+// instruments it has created or will create, are recreated automatically from
+// the new MeterProvider.
+//
+// This is short for GetMeterProvider().Meter(name).
+func Meter(name string, opts ...metric.MeterOption) metric.Meter {
+	// TODO (#3819): Remove this disablement.
+	// nolint: staticcheck  // Temporary, while metric/global is deprecated.
+	return GetMeterProvider().Meter(name, opts...)
+}
+
+// GetMeterProvider returns the registered global meter provider.
+//
+// If no global GetMeterProvider has been registered, a No-op GetMeterProvider
+// implementation is returned. When a global GetMeterProvider is registered for
+// the first time, the returned GetMeterProvider, and all the Meters it has
+// created or will create, are recreated automatically from the new
+// GetMeterProvider.
+func GetMeterProvider() metric.MeterProvider {
+	// TODO (#3819): Remove this disablement.
+	// nolint: staticcheck  // Temporary, while metric/global is deprecated.
+	return global.MeterProvider()
+}
+
+// SetMeterProvider registers mp as the global MeterProvider.
+func SetMeterProvider(mp metric.MeterProvider) {
+	// TODO (#3819): Remove this disablement.
+	// nolint: staticcheck  // Temporary, while metric/global is deprecated.
+	global.SetMeterProvider(mp)
+}