Prevent upscaling

**Glide Version**: 4.12.0

**Integration libraries**: No, it's a sandbox project to isolate the issue.

**Device/Android Version**: Google Pixel 3XL, Android 11

**Issue details / Repro steps / Use case background**:
What I want sounds rather simple. I don't want images to get upscaled. I'm fine with downscaling which is an obvious thing to expect with such a library but if the image is too small, I don't want it upscaled to fit the bounds of the `ImageView` since it looks pixelated.

**Glide load line / `GlideModule` (if any) / list Adapter code (if any)**:
```java
Glide.with(this)
.load(URL)
.downsample(DownsampleStrategy.CENTER_INSIDE)
.into(imageView)
```

**Layout XML**:
```xml

```

**Stack trace / LogCat**:
N/A