List Tables: Arrange action items into a grid with extra space.

On small screens, list table actions were cramped. This makes it easy to press the wrong action by mistake. The items are now arranged into a grid and given extra room to create a larger tap-target.

The plugins list table was excluded because it's current layout doesn't match the others, and we should add more space to this in a future commit.

Props jobthomas, ryelle.
Fixes #45024.

Built from https://develop.svn.wordpress.org/trunk@43670


git-svn-id: https://core.svn.wordpress.org/trunk@43499 1a063a9b-81f0-0310-95a4-ce76da25c4cd