Disable drag on images to enable multi-select

[ellatrix]

This may be a bit controversial, but in order to enable multi-select starting at image blocks with the current behaviour, we need to disable dragging them. Dragging in the current WP core editor is used to move the image. We now have the block movers for this, and it make be better to find a solution for drag-and-drop for all blocks that is consistent rather than images alone. (Also note that dragging the images will not work to move them at the moment, it would have to be implemented. You can drag it in an Editable region though...)

[jasmussen]

I think it's probably for the best to disable dragging regardless, at least for a block such as the image block. It's something that we could consider enabling for the freeform block.

Selecting starting at the image works as intended, nice!

I'm seeing the focus style on the trash button permanently:

Is the blue selection header not in master yet? Not seeing it here.

The flickering when selecting across blocks, I can't tell if it got worse in this PR or not. But it's definitely something we'll want to look at at some point.

Otherwise, works well!

[ellatrix]

I almost forgot: I should note that this disables any kind of dragging from inside the block, also text dragging. Notice that in master you can select some text, and then drag the selected text to another Editable region. Not sure if we should disable that. Maybe we should do some filtering based on the target.

[ellatrix]

The header thing is still in #955. Yeah, I should look at the flickering next.

[mtias]

I like this behaviour, it's more consistent with what we are building, and make our core interactions more reliable.

[aduth]

Maybe we should do some filtering based on the target.

Prevent by nodeType === Node.ELEMENT_NODE ?

[ellatrix]

Interesting. event.nativeEvent.target is not the same as event.target. React seems to give the parent node for text nodes. Checking if the target is a text node may be reliable. I'd think the data would be at least plain text, but the browser even wraps it in a span with styles (drag quote inside citation). This will probably fixed together with cleaning pasted content.

[ellatrix]

(If React adjusts the target, it may mean that it's not consistent across browsers. Looking.)

[ellatrix]

https://github.com/facebook/react/blob/v16.0.0-alpha.3/src/renderers/dom/shared/utils/getEventTarget.js#L29

[ellatrix]

Let's ignore all for now.