@uppy/thumbnail-generator: don't enlarge already small thumbnails (#4406)

- Thumbnail shouldn’t be enlarged / upscaled, only reduced. If img is
already smaller than width/height, leave it as is. @nqst reported this
in
https://github.com/transloadit/uppy/pull/4374#pullrequestreview-1361065165
- We have image width/height when we resize for thumbnail, might as well
set it as file.meta for Uppy users and us to use in the UI?

Before:
![Screen Shot 2023-04-07 at 01 57
55](https://user-images.githubusercontent.com/1199054/230519313-ac8c86e1-4c04-4f9d-a19b-480e0215452f.png)

After:
![Screen Shot 2023-04-07 at 01 56
55](https://user-images.githubusercontent.com/1199054/230519337-55890d39-8091-4038-b897-483e452fcf55.png)

---------

Co-authored-by: Mikael Finstad <finstaden@gmail.com>
Co-authored-by: Merlijn Vos <merlijn@soverin.net>

.changeset/warm-bulldogs-relate.md

@@ -0,0 +1,5 @@
+---
+"@uppy/thumbnail-generator": patch
+---
+
+Make tiny/small thumbnails look better by not scaling them to cover the entire grid item

packages/@uppy/thumbnail-generator/src/index.ts

@@ -258,16 +258,23 @@ export default class ThumbnailGenerator<
     }
 
     if (width != null) {
+      let targetWidth = width
+      // Thumbnail shouldn’t be enlarged / upscaled, only reduced.
+      // If img is already smaller than width/height, leave it as is.
+      if (img.width < width) targetWidth = img.width
+
       return {
-        width,
-        height: Math.round(width / aspect),
+        width: targetWidth,
+        height: Math.round(targetWidth / aspect),
       }
     }
 
     if (height != null) {
+      let targetHeight = height
+      if (img.height < height) targetHeight = img.height
       return {
-        width: Math.round(height * aspect),
-        height,
+        width: Math.round(targetHeight * aspect),
+        height: targetHeight,
       }
     }