[sdk-metrics] Use FrozenSet when looking up explicit bounds (open-telemetry#5899)

Co-authored-by: Mikel Blanchard <[email protected]>

Author: joegoldman2

src/OpenTelemetry/Metrics/Metric.cs

@@ -1,6 +1,9 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+#if NET
+using System.Collections.Frozen;
+#endif
 using System.Diagnostics.Metrics;
 
 namespace OpenTelemetry.Metrics;
@@ -18,7 +21,13 @@ public sealed class Metric
 
     // Short default histogram bounds. Based on the recommended semantic convention values for http.server.request.duration.
     internal static readonly double[] DefaultHistogramBoundsShortSeconds = new double[] { 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 };
-    internal static readonly HashSet<(string, string)> DefaultHistogramBoundShortMappings = new()
+    internal static readonly
+#if NET
+    FrozenSet<(string, string)>
+#else
+    HashSet<(string, string)>
+#endif
+    DefaultHistogramBoundShortMappings = new HashSet<(string, string)>
     {
         ("Microsoft.AspNetCore.Hosting", "http.server.request.duration"),
         ("Microsoft.AspNetCore.RateLimiting", "aspnetcore.rate_limiting.request.time_in_queue"),
@@ -30,16 +39,30 @@ public sealed class Metric
         ("System.Net.Http", "http.client.request.duration"),
         ("System.Net.Http", "http.client.request.time_in_queue"),
         ("System.Net.NameResolution", "dns.lookup.duration"),
-    };
+    }
+#if NET
+    .ToFrozenSet()
+#endif
+    ;
 
     // Long default histogram bounds. Not based on a standard. May change in the future.
     internal static readonly double[] DefaultHistogramBoundsLongSeconds = new double[] { 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60, 120, 300 };
-    internal static readonly HashSet<(string, string)> DefaultHistogramBoundLongMappings = new()
+    internal static readonly
+#if NET
+    FrozenSet<(string, string)>
+#else
+    HashSet<(string, string)>
+#endif
+    DefaultHistogramBoundLongMappings = new HashSet<(string, string)>
     {
         ("Microsoft.AspNetCore.Http.Connections", "signalr.server.connection.duration"),
         ("Microsoft.AspNetCore.Server.Kestrel", "kestrel.connection.duration"),
         ("System.Net.Http", "http.client.connection.duration"),
-    };
+    }
+#if NET
+    .ToFrozenSet()
+#endif
+    ;
 
     internal readonly AggregatorStore AggregatorStore;