Update mixin that sets hover style on some buttons

[enriquesanchez]

Fixes #17337

This is a small update to the button-style__hover mixin in _mixins.scss. The change makes the hover style match the "hard line" style used on the block toolbar and the "Settings" and "More tools & options".

Some nitpicks

This change makes more noticeable the size/padding difference between the top toolbar and block toolbar buttons that was already present. Not sure if it's worth looking at this, thoughts?

We also have another hover style in the block inserter, should we also look at updating this one?

[mapk]

I really like the consistency here, @enriquesanchez! Thanks for taking this on!

I also noticed that this PR updates these as well, which is excellent.

[mapk]

It also updated it here too:

One thing to note for another PR is the "Block Navigation" popover hover state AND the block's "More Options" popover hover state don't match the rest of the popover hover states. We'll need to create another PR for this.

... that is... if we want this hover state to perpetuate into the popover menus. After looking at it more, I'm inclined to keep the grey solid hover states for the popover menus. It's great on the icons though.

[enriquesanchez]

Thanks for the feedback @mapk!

I've created another PR (#17621) to address the hover styles of the dropdown menus.

[karmatosed]

Should buttons have the style that is coming from core over the hardline? Specifically, the publish button.

[enriquesanchez]

@karmatosed I'm not sure. Think that can be explored on another issue? Particularly if it refers to the Publish button.

[enriquesanchez]

@mapk I added the styles to match the updates from #17621, which has already been merged. Would you mind giving it a second look just to be safe?

[mapk]

Just tested again, @enriquesanchez and it works really well. It has removed the original hover effect which would have been odd keeping and now shows the lighter grey. Thanks! 👍