focus not preserved after keyboard or block select events

The block focus is not preserved after keyboard events or if a different block is selected. (This will cause issues with apps that use CSS to highlight the currently focused block).

This is similar to [issue#1124](https://github.com/codex-team/editor.js/issues/1124), but occurs under several other circumstances.

Steps to reproduce:
1. display any doc in EditorJS
2. click or tab to any block, or enter text via keyboard

Expected behavior:
The currently selected block should have a style of "ce-block--focused" but it doesn't.

Device, Browser, OS:
Firefox 75.0, Ubuntu 20.04 (doesn't matter)

Editor.js version:
2.17.0/2.18.0

The fix is to set the focus again after mouse or keyboard events are processed or a new block is selected.