Load content to buffer before attempting deserialization (#1705)

* Load content to buffer before attempting deserialization to ensure raw content can be captured in ApiException if an exception occurs during deserialization

* Ensure stream is seekable before attempting to load into buffer

---------

Co-authored-by: Chris Pulman <chris.pulman@yahoo.com>

Refit.Tests/ResponseTests.cs

@@ -511,6 +511,7 @@ public sealed class ThrowOnGetLengthMemoryStream : MemoryStream
 {
     public bool CanGetLength { get; set; }
 
+    public override bool CanSeek { get => CanGetLength; }
     public override long Length =>
         CanGetLength ? base.Length : throw new NotSupportedException();
 }

Refit/RequestBuilderImplementation.cs

@@ -452,6 +452,13 @@ CancellationToken cancellationToken
             }
             else
             {
+                using var stream = await content
+                    .ReadAsStreamAsync(cancellationToken)
+                    .ConfigureAwait(false);
+                if (stream.CanSeek)
+                {
+                    await content.LoadIntoBufferAsync().ConfigureAwait(false);
+                }
                 result = await serializer
                     .FromHttpContentAsync<T>(content, cancellationToken)
                     .ConfigureAwait(false);