Gallery Block: Drag and drop multiple images create a gallery block

[youknowriad]

closes #3364

This PR adds a "transformation" to allow drag and dropping multiple images to the editor canvas in order to create a gallery block.

This doesn't solve the lack of feedback while the upload is in progress, this issue is not specific to the gallery block and I believe is tracked in a separate issue.

Testing instructions

• Drag multiple images to the editor canvas
• After the images upload, A gallery block should appear.

[jasmussen]

This works great! Really really killer feature, this. Nice work.

The missing upload feedback would be nice to address for both images and galleries, but as you say, doesn't have to be this PR.

Can we tweak the "drop files to upload" stuff a little bit? The icon isn't critically necessary, and a 13px default font would be nice. And if you can use $medium-blue-500 for the bg color, that would be stellar:

[youknowriad]

Can we tweak the "drop files to upload" stuff a little bit? The icon isn't critically necessary, and a 13px default font would be nice. And if you can use $medium-blue-500 for the bg color, that would be stellar

This placeholder is the same used elsewhere images, galleries etc... Are you suggesting we tweak it only for the empty post use-case? (your screenshot)

Also, I think the background color has been changed at some point to match the Accessibility guidelines.

[jasmussen]

If there's a solid reason why the upload message looks like that, it's okay for us to keep it unchanged. But it seems like it's at least inheriting the body font, so it might be the case that it should be using a different font at least.

CC: @afercia can you recall details around this?

[youknowriad]

I've forced the default font for the dropzone and removed the icon but only for the empty post placeholder's dropzone. I think it's better now.

[jasmussen]

🎉

Looks good, design wise.