Update function docs in sdk.go (open-telemetry#1826)

* Made copy of attribute.KeyValue

* Add comments and test

* move test to sdk/metric

* Update CHANGELOG.md

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>

* Add label order assertions for final results

* Update CHANGELOG PR number

* Revert code changes and update docs

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

sdk/metric/sdk.go

@@ -282,10 +282,12 @@ func (s *syncInstrument) acquireHandle(kvs []attribute.KeyValue, labelPtr *attri
 	}
 }
 
+// The order of the input array `kvs` may be sorted after the function is called.
 func (s *syncInstrument) Bind(kvs []attribute.KeyValue) metric.BoundSyncImpl {
 	return s.acquireHandle(kvs, nil)
 }
 
+// The order of the input array `kvs` may be sorted after the function is called.
 func (s *syncInstrument) RecordOne(ctx context.Context, num number.Number, kvs []attribute.KeyValue) {
 	h := s.acquireHandle(kvs, nil)
 	defer h.Unbind()
@@ -396,6 +398,7 @@ func (m *Accumulator) collectSyncInstruments() int {
 }
 
 // CollectAsync implements internal.AsyncCollector.
+// The order of the input array `kvs` may be sorted after the function is called.
 func (m *Accumulator) CollectAsync(kv []attribute.KeyValue, obs ...metric.Observation) {
 	labels := attribute.NewSetWithSortable(kv, &m.asyncSortSlice)
 
@@ -472,6 +475,7 @@ func (m *Accumulator) checkpointAsync(a *asyncInstrument) int {
 }
 
 // RecordBatch enters a batch of metric events.
+// The order of the input array `kvs` may be sorted after the function is called.
 func (m *Accumulator) RecordBatch(ctx context.Context, kvs []attribute.KeyValue, measurements ...metric.Measurement) {
 	// Labels will be computed the first time acquireHandle is
 	// called.  Subsequent calls to acquireHandle will re-use the