make intializer for metadata even nicer

src/csharp/Grpc.Core.Tests/ClientServerTest.cs

@@ -190,8 +190,8 @@ namespace Grpc.Core.Tests
 
             var headers = new Metadata
             {
-                new Metadata.Entry("ascii-header", "abcdefg"),
-                new Metadata.Entry("binary-header-bin", new byte[] { 1, 2, 3, 0, 0xff }),
+                { "ascii-header", "abcdefg" },
+                { "binary-header-bin", new byte[] { 1, 2, 3, 0, 0xff } }
             };
             var call = Calls.AsyncUnaryCall(helper.CreateUnaryCall(new CallOptions(headers: headers)), "ABC");
             await call;

src/csharp/Grpc.Core.Tests/CompressionTest.cs

@@ -94,7 +94,7 @@ namespace Grpc.Core.Tests
 
                 context.WriteOptions = new WriteOptions(WriteFlags.NoCompress);
 
-                await context.WriteResponseHeadersAsync(new Metadata { new Metadata.Entry("ascii-header", "abcdefg") });
+                await context.WriteResponseHeadersAsync(new Metadata { { "ascii-header", "abcdefg" } });
 
                 await responseStream.WriteAsync("X");
 

src/csharp/Grpc.Core.Tests/Internal/MetadataArraySafeHandleTest.cs

@@ -53,8 +53,8 @@ namespace Grpc.Core.Internal.Tests
         {
             var metadata = new Metadata
             {
-                new Metadata.Entry("host", "somehost"),
-                new Metadata.Entry("header2", "header value"),
+                { "host", "somehost" },
+                { "header2", "header value" },
             };
             var nativeMetadata = MetadataArraySafeHandle.Create(metadata);
             nativeMetadata.Dispose();
@@ -65,8 +65,8 @@ namespace Grpc.Core.Internal.Tests
         {
             var metadata = new Metadata
             {
-                new Metadata.Entry("host", "somehost"),
-                new Metadata.Entry("header2", "header value"),
+                { "host", "somehost" },
+                { "header2", "header value" }
             };
             var nativeMetadata = MetadataArraySafeHandle.Create(metadata);
 

src/csharp/Grpc.Core.Tests/ResponseHeadersTest.cs

@@ -63,10 +63,7 @@ namespace Grpc.Core.Tests
             server.Start();
             channel = helper.GetChannel();
 
-            headers = new Metadata
-            {
-                new Metadata.Entry("ascii-header", "abcdefg"),
-            };
+            headers = new Metadata { { "ascii-header", "abcdefg" } };
         }
 
         [TearDown]

src/csharp/Grpc.Core/Metadata.cs

@@ -114,6 +114,16 @@ namespace Grpc.Core
             entries.Add(item);
         }
 
+        public void Add(string key, string value)
+        {
+            Add(new Entry(key, value));
+        }
+
+        public void Add(string key, byte[] valueBytes)
+        {
+            Add(new Entry(key, valueBytes));
+        }
+
         public void Clear()
         {
             CheckWriteable();