Focus mode

[Enter-tainer]

Add an indicator to latest edited place, or highlight it.

[Myriad-Dreamin]

Idea1: add a visual cursor in preview panel corresponding to the cursor in editor.

• add related event, Focus mode part1: add cursor events #157
• compiler produces more accurate position for cursor
• bikeshielding: design nice default cursor
  • or feature to customize cursor

Idea2: add faded-out mask to not focused elements.
See https://zhuanlan.zhihu.com/p/660899445?utm_psn=1695959995928170496