Merge from main.

src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSourceActivity.cs

@@ -443,10 +443,12 @@ public sealed class InstrumentAdvice<T> where T : struct
     public delegate void MeasurementCallback<T>(Instrument instrument, T measurement, ReadOnlySpan<System.Collections.Generic.KeyValuePair<string, object?>> tags, object? state) where T : struct;
     public class Meter : IDisposable
     {
-        public Counter<T> CreateCounter<T>(string name, string? unit = null, string? description = null) where T : struct  { throw null; }
-        public Counter<T> CreateCounter<T>(string name, string? unit, string? description, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object?>> tags) where T : struct  { throw null; }
-        public UpDownCounter<T> CreateUpDownCounter<T>(string name, string? unit = null, string? description = null) where T : struct  { throw null; }
-        public UpDownCounter<T> CreateUpDownCounter<T>(string name, string? unit, string? description, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object?>> tags) where T : struct  { throw null; }
+        public Counter<T> CreateCounter<T>(string name, string? unit = null, string? description = null) where T : struct { throw null; }
+        public Counter<T> CreateCounter<T>(string name, string? unit, string? description, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object?>> tags) where T : struct { throw null; }
+        public Gauge<T> CreateGauge<T>(string name) where T : struct { throw null; }
+        public Gauge<T> CreateGauge<T>(string name, string? unit = null, string? description = null, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object?>>? tags = null) where T : struct { throw null; }
+        public UpDownCounter<T> CreateUpDownCounter<T>(string name, string? unit = null, string? description = null) where T : struct { throw null; }
+        public UpDownCounter<T> CreateUpDownCounter<T>(string name, string? unit, string? description, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object?>> tags) where T : struct { throw null; }
         public Histogram<T> CreateHistogram<T>(string name) where T : struct { throw null; }
         [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)]
         public Histogram<T> CreateHistogram<T>(string name, string? unit, string? description) where T : struct { throw null; }