Revert "Make PixelTypeInfo a struct"

This reverts commit 9269aac086.

src/ImageSharp/Formats/PixelTypeInfo.cs

@@ -6,10 +6,10 @@ namespace SixLabors.ImageSharp.Formats
     /// <summary>
     /// Contains information about the pixels that make up an images visual data.
     /// </summary>
-    public readonly struct PixelTypeInfo
+    public class PixelTypeInfo
     {
         /// <summary>
-        /// Initializes a new instance of the <see cref="PixelTypeInfo"/> struct.
+        /// Initializes a new instance of the <see cref="PixelTypeInfo"/> class.
         /// </summary>
         /// <param name="bitsPerPixel">Color depth, in number of bits per pixel.</param>
         internal PixelTypeInfo(int bitsPerPixel)

tests/ImageSharp.Tests/Formats/Bmp/BmpDecoderTests.cs

@@ -57,7 +57,7 @@ namespace SixLabors.ImageSharp.Tests
             var testFile = TestFile.Create(imagePath);
             using (var stream = new MemoryStream(testFile.Bytes, false))
             {
-                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType.BitsPerPixel);
+                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType?.BitsPerPixel);
             }
         }
     }

tests/ImageSharp.Tests/Formats/Gif/GifDecoderTests.cs

@@ -172,7 +172,7 @@ namespace SixLabors.ImageSharp.Tests
             TestFile testFile = TestFile.Create(imagePath);
             using (var stream = new MemoryStream(testFile.Bytes, false))
             {
-                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType.BitsPerPixel);
+                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType?.BitsPerPixel);
             }
         }
 

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.cs

@@ -397,10 +397,10 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
         [InlineData(TestImages.Jpeg.Baseline.Snake, 24)]
         public void DetectPixelSize(string imagePath, int expectedPixelSize)
         {
-            var testFile = TestFile.Create(imagePath);
+            TestFile testFile = TestFile.Create(imagePath);
             using (var stream = new MemoryStream(testFile.Bytes, false))
             {
-                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType.BitsPerPixel);
+                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType?.BitsPerPixel);
             }
         }
     }

tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs

@@ -228,10 +228,10 @@ namespace SixLabors.ImageSharp.Tests
         [InlineData(TestImages.Png.Rgb48BppInterlaced, 48)]
         public void DetectPixelSize(string imagePath, int expectedPixelSize)
         {
-            var testFile = TestFile.Create(imagePath);
+            TestFile testFile = TestFile.Create(imagePath);
             using (var stream = new MemoryStream(testFile.Bytes, false))
             {
-                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType.BitsPerPixel);
+                Assert.Equal(expectedPixelSize, Image.Identify(stream)?.PixelType?.BitsPerPixel);
             }
         }