Use string interpolation in a few more places (#82096)

Places where we'd otherwise be allocating for at least one of the subcomponents.

src/libraries/System.Formats.Asn1/src/System/Formats/Asn1/Asn1Tag.cs

@@ -472,7 +472,7 @@ public override string ToString()
             }
             else
             {
-                classAndValue = TagClass + "-" + TagValue;
+                classAndValue = $"{TagClass}-{TagValue}";
             }
 
             if (IsConstructed)

src/libraries/System.Net.Mail/src/System/Net/Mail/SmtpClient.cs

@@ -272,7 +272,7 @@ public ServicePoint ServicePoint
                 // be usable, whereas in .NET Framework it throws an exception that "This property is not supported for
                 // protocols that do not use URI."
 #pragma warning disable SYSLIB0014
-                return _servicePoint ??= ServicePointManager.FindServicePoint(new Uri("mailto:" + _host + ":" + _port));
+                return _servicePoint ??= ServicePointManager.FindServicePoint(new Uri($"mailto:{_host}:{_port}"));
 #pragma warning restore SYSLIB0014
             }
         }

src/libraries/System.Net.Requests/src/System/Net/HttpWebRequest.cs

@@ -352,7 +352,7 @@ public string Host
                 Uri hostUri = _hostUri ?? Address;
                 return (_hostUri == null || !_hostHasPort) && Address.IsDefaultPort ?
                     hostUri.Host :
-                    hostUri.Host + ":" + hostUri.Port;
+                    $"{hostUri.Host}:{hostUri.Port}";
             }
             set
             {

src/libraries/System.Net.ServicePoint/src/System/Net/ServicePointManager.cs

@@ -197,8 +197,8 @@ private static bool ProxyAddressIfNecessary(ref Uri address, IWebProxy? proxy)
         }
 
         private static string MakeQueryString(Uri address) => address.IsDefaultPort ?
-            address.Scheme + "://" + address.DnsSafeHost :
-            address.Scheme + "://" + address.DnsSafeHost + ":" + address.Port.ToString();
+            $"{address.Scheme}://{address.DnsSafeHost}" :
+            $"{address.Scheme}://{address.DnsSafeHost}:{address.Port}";
 
         private static string MakeQueryString(Uri address, bool isProxy)
         {

src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/ActivityTracker.cs

@@ -264,7 +264,7 @@ private static string NormalizeActivityName(string providerName, string activity
             }
             else if (task != 0)
             {
-                return providerName + "task" + task.ToString();
+                return $"{providerName}task{task}";
             }
             else
             {

src/libraries/System.Reflection.DispatchProxy/src/System/Reflection/DispatchProxyGenerator.cs

@@ -220,7 +220,7 @@ private ProxyBuilder CreateProxy(
                 [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type proxyBaseType)
             {
                 int nextId = Interlocked.Increment(ref _typeId);
-                TypeBuilder tb = _mb.DefineType(name + "_" + nextId, TypeAttributes.Public, proxyBaseType);
+                TypeBuilder tb = _mb.DefineType($"{name}_{nextId}", TypeAttributes.Public, proxyBaseType);
                 return new ProxyBuilder(this, tb, proxyBaseType);
             }