Fix spacer block resizing

[noisysocks]

Fixes #7755.

The sibling inserter was preventing a user from being able to resize the spacer using the top drag handle.

To test:

1. Insert a spacer block
2. Check that it can be resized using both drag handles
3. Insert an image block
4. Check that it can be resized using both drag handles

[mcsf]

Thanks for looking into this. Unfortunately, this way, one can't get to the upper sibling inserter when selecting a Spacer block.

P.S.: Edited the PR description to fix the "Fixes #xxxx" against the correct issue.

[ZebulanStanphill]

Would it make more sense to just remove the drag handle from the top of the Spacer block? There is not really a need for one on both the top and bottom, and dragging from the top works a little oddly.

[mcsf]

cc @jasmussen

[noisysocks]

Doh, I totally missed that. 🤦‍♂️

I've updated this PR to remove the top resize handle altogether:

[mcsf]

@noisysocks: thanks, though the upper sibling inserter is still inaccessible. :)

[noisysocks]

🤔 perhaps this is intentional? @jasmussen?

It looks like, in master, the sibling inserter never shows when you hover over the top of the selected block, unless Fix Toolbar to Top is enabled.

[jasmussen]

This is intentional for the sibling inserter when a block is selected and that block has no toolbar to cover the sibling inserter.

It seems this aspect is non optimal when a block has no toolbar, as in the case of the spacer. As we look for a way to fix this let's be sure to not regress this sibling inserter behavior for blocks with toolbars.

[jasmussen]

And by the way I thing it's fine to simply not show the top resizing handle. Your mouse is floating in air anyway, when you use it.

[noisysocks]

I think then let's leave this as is. We can look at making the sibling inserter appear when the block has no toolbar in a seperate PR. Issue here: #7884

[mcsf]

Thanks for fixing!