[bugfix] Downstep otel to fix freebsd compile issue (#1773)

https://github.com/open-telemetry/opentelemetry-go/issues/4076

vendor/go.opentelemetry.io/otel/metric/instrument/instrument.go

@@ -0,0 +1,88 @@
+// 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 instrument // import "go.opentelemetry.io/otel/metric/instrument"
+
+// Asynchronous instruments are instruments that are updated within a Callback.
+// If an instrument is observed outside of it's callback it should be an error.
+//
+// This interface is used as a grouping mechanism.
+type Asynchronous interface {
+	asynchronous()
+}
+
+// Synchronous instruments are updated in line with application code.
+//
+// This interface is used as a grouping mechanism.
+type Synchronous interface {
+	synchronous()
+}
+
+// Option applies options to all instruments.
+type Option interface {
+	Float64ObserverOption
+	Int64ObserverOption
+	Float64Option
+	Int64Option
+}
+
+type descOpt string
+
+func (o descOpt) applyFloat64(c Float64Config) Float64Config {
+	c.description = string(o)
+	return c
+}
+
+func (o descOpt) applyInt64(c Int64Config) Int64Config {
+	c.description = string(o)
+	return c
+}
+
+func (o descOpt) applyFloat64Observer(c Float64ObserverConfig) Float64ObserverConfig {
+	c.description = string(o)
+	return c
+}
+
+func (o descOpt) applyInt64Observer(c Int64ObserverConfig) Int64ObserverConfig {
+	c.description = string(o)
+	return c
+}
+
+// WithDescription sets the instrument description.
+func WithDescription(desc string) Option { return descOpt(desc) }
+
+type unitOpt string
+
+func (o unitOpt) applyFloat64(c Float64Config) Float64Config {
+	c.unit = string(o)
+	return c
+}
+
+func (o unitOpt) applyInt64(c Int64Config) Int64Config {
+	c.unit = string(o)
+	return c
+}
+
+func (o unitOpt) applyFloat64Observer(c Float64ObserverConfig) Float64ObserverConfig {
+	c.unit = string(o)
+	return c
+}
+
+func (o unitOpt) applyInt64Observer(c Int64ObserverConfig) Int64ObserverConfig {
+	c.unit = string(o)
+	return c
+}
+
+// WithUnit sets the instrument unit.
+func WithUnit(u string) Option { return unitOpt(u) }