Always show side inserter on the last empty paragraph

[youknowriad]

This is a proposal to try to tweak the block inserter visibility. Some feedback suggest that it's not always clear how to add blocks/content.

in this PR, I'm trying to give more visibility to the side block inserter on the last paragraph of the post content. Also when focusing "empty paragraphs", we always show the inserter.

[mtias]

This is looking better. A few points:

• Let's keep the quick-shortcuts separate until we figure out their role.
• When you hit enter on a paragraph block, we should still show the + on the new line.

[jasmussen]

I appreciate this effort, and would echo Matías thoughts: the quick shortcuts don't shine so maybe keep those as they were until we figure something better. Plus, consistency is good.

With that in place, this change seems like it could be a good way to move us forward with making it easy to insert blocks between content and at the end of content. Despite my desire to use Enter as the primary way to do so, this has worked less well in practice than I'd hoped. And I do prefer this side inserter over the sibling inserter, still :D

That said, this still feels sort of like a half-step. I suspect that it would be good for us to continue to think about more profound steps to make it simple to append content. I imagine answers might even present themselves more clearly if/when block areas becomes more of a thing.

[youknowriad]

The shortcuts change was unintended :)
I made some adjustments, let me know how it feels.

[kjellr]

This feels good to me:

The only sort of awkward part is when you have two empty paragraphs in a row, you get double add buttons on hover. I think that's okay though:

I also tried on columns  — if you manually add a bunch of empty paragraph blocks, they'll all have Add buttons too. But this seems fine as well:

Sounds like both of the points from @mtias have been addressed, so I think this is good to go for now. I agree with @jasmussen though that we should continue thinking up ways to improve this moving forward.