[MM-62191] Remove disintegration/imaging dependency (#29657)

* Remove disintegration/imaging dependency

* Simplify FillCenter logic

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/imaging/preview_test.go

@@ -5,8 +5,10 @@ package imaging
 
 import (
 	"image"
+	"image/color"
 	"testing"
 
+	"github.com/anthonynsimon/bild/transform"
 	"github.com/stretchr/testify/require"
 )
 
@@ -75,3 +77,96 @@ func TestGenerateThumbnail(t *testing.T) {
 		})
 	}
 }
+
+func createTestImage(t *testing.T, width, height int) image.Image {
+	t.Helper()
+	img := image.NewNRGBA(image.Rect(0, 0, width, height))
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+			img.Set(x, y, color.NRGBA{uint8(x % 256), uint8(y % 256), 0, 255})
+		}
+	}
+	return img
+}
+
+func TestResize(t *testing.T) {
+	for _, tc := range []struct {
+		name      string
+		img       image.Image
+		targetW   int
+		targetH   int
+		expectedW int
+		expectedH int
+	}{
+		{
+			name:      "zero target dimensions",
+			img:       createTestImage(t, 100, 50),
+			targetW:   0,
+			targetH:   0,
+			expectedW: 0,
+			expectedH: 0,
+		},
+		{
+			name:      "negative target dimensions",
+			img:       createTestImage(t, 100, 50),
+			targetW:   -1,
+			targetH:   25,
+			expectedW: 0,
+			expectedH: 0,
+		},
+		{
+			name:      "zero source dimensions",
+			img:       createTestImage(t, 0, 0),
+			targetW:   50,
+			targetH:   25,
+			expectedW: 0,
+			expectedH: 0,
+		},
+		{
+			name:      "preserve aspect ratio with width",
+			img:       createTestImage(t, 100, 50),
+			targetW:   50,
+			targetH:   0,
+			expectedW: 50,
+			expectedH: 25,
+		},
+		{
+			name:      "preserve aspect ratio with width, height > width",
+			img:       createTestImage(t, 50, 100),
+			targetW:   50,
+			targetH:   0,
+			expectedW: 50,
+			expectedH: 100,
+		},
+		{
+			name:      "preserve aspect ratio with height",
+			img:       createTestImage(t, 100, 50),
+			targetW:   0,
+			targetH:   25,
+			expectedW: 50,
+			expectedH: 25,
+		},
+		{
+			name:      "preserve aspect ratio with height, height > width",
+			img:       createTestImage(t, 50, 100),
+			targetW:   0,
+			targetH:   25,
+			expectedW: 13,
+			expectedH: 25,
+		},
+		{
+			name:      "valid target dimensions",
+			img:       createTestImage(t, 100, 50),
+			targetW:   50,
+			targetH:   25,
+			expectedW: 50,
+			expectedH: 25,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			resizedImg := Resize(tc.img, tc.targetW, tc.targetH, transform.Lanczos)
+			require.Equal(t, tc.expectedW, resizedImg.Bounds().Dx())
+			require.Equal(t, tc.expectedH, resizedImg.Bounds().Dy())
+		})
+	}
+}