fix: adjust CvFileUploader drop handler to not ignore 'multiple' attribute

[felipebritor]

Contributes to #1663

What did you do?

Update 'drop' event handler, at CvFileUploader, to handle files considering 'multiple' attribute

Why did you do it?

Fix the drop behavior when multiple is falsy

How have you tested it?

Yes. Automated tests also added.

Were docs updated if needed?

• N/A
• No
• Yes

[davidnixon]

@felipebritor a tweak is still needed.

1. This does prevent me from selecting multiple files and dropping them on the target. When I do that I only get 1 file as expected. ✅
2. I can however drag and drop a file and then drag and drop another file so that now there are two! ❌
3. The multiple attribute should default to true ❌
4. The React story is unclear on how the button mode (non drag & drop mode) should work. I wonder if you or @themoenen has an opinion on that?

Referencing the same component in res=act:
https://react.carbondesignsystem.com/?path=/story/components-fileuploader--drag-and-drop-upload-container-example-application&args=multiple:!false

[felipebritor]

@felipebritor a tweak is still needed.

1. This does prevent me from selecting multiple files and dropping them on the target. When I do that I only get 1 file as expected. ✅
2. I can however drag and drop a file and then drag and drop another file so that now there are two! ❌
3. The multiple attribute should default to true ❌
4. The React story is unclear on how the button mode (non drag & drop mode) should work. I wonder if you or @themoenen has an opinion on that?

Referencing the same component in res=act: https://react.carbondesignsystem.com/?path=/story/components-fileuploader--drag-and-drop-upload-container-example-application&args=multiple:!false

Regarding your points:
2. Sorry about it, David. Fixed
3. Added to PR. Had to turn multiple into a props for it
4. I think it does here. Or did you mean something else?

[davidnixon]

Thanks!! LGTM