Remove unused is-hovered class

[ellatrix]

Description

This PR removed the is-hovered class on blocks when hovering over them. The styles had been removed in #18862.

It also removes the hover state in the block, which is only used for one thing: showing the side block inserter when the default block is empty. I would suggest to either:

• Only show it when the block is selected or last (as before, just not on hover).
• Show it all the time.

I chose the first option, but I don't mind changing it.

One aspect of removing the hover effect is that it is intrinsically a desktop affordance, and one that is very much biased towards sighted users. Removing it might help us rely on other affordances that are more cross-platform and potentially, accessible.

-- @jasmussen

It's also worth noting that this removes a number of event handlers that are added to every single block.

Also reverts 0d0c8e0 (from #5658) because this is no longer needed.

How has this been tested?

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR. .

[aduth]

I think this was the only usage of the "Handled" behavior for IgnoreNestedEvents, so it could be removed. Not sure that it will make a ton of difference, but at least simplifying a bit.

Effectively would amount to a revert of 0d0c8e0d55849529227df3540ad35ff3edf5be5b (from #5658)

[ellatrix]

I think this is a sensible change. If you create a new (empty) paragraph, it is selected, and you'll see the side inserter. If you select another block, the side inserter is gone. It makes sense to select the block again to see the side inserter. Additionally, there's the in-between inserters which are consistently available for every block on hover.