Apply keyboard shortcuts & input rules to selections

[matthewlipski]

Currently, keyboard shortcuts, input rules, and the block type dropdown doesn't work properly when a selection is active. The keyboard shortcuts and input rules only apply to the first block while the block type dropdown applies to nested blocks and also applies to blocks with content types other than inline*.

Selections need to be fixed to ignore child blocks (and have other inconsistent behaviour), while the commands themselves should ignore blocks with content types other than inline*.