Editor: Don't move focus to the editor when switching editor mode

[shrivastavanolo]

Previously, switching between Visual and Text mode would unconditionally move focus into the destination editor (via editor.focus() / textArea.focus()), because the selection-bookmark mechanism used to preserve cursor position across the switch is populated almost every time, regardless of whether the source field was actually focused.

In the common case — clicking the Visual/Text tab — focus has already moved to that tab button by the time the switch handler runs, so forcibly focusing the editor content area pulls focus away from the control the user just activated. This is disruptive for keyboard and assistive technology users, who lose their place in the document unexpectedly.

Now, focus is only moved into the destination editor if the source field already had focus when the switch was triggered (e.g. a keyboard shortcut fired while actively editing). The cursor/selection position is still restored either way, so it's correct if the user does click into the field afterward — only the automatic focus-stealing (and the accompanying scroll-into-view, which would otherwise move the page without moving focus) is skipped.

Trac ticket: https://core.trac.wordpress.org/ticket/42540

Use of AI Tools

AI assistance: Yes
Tool(s): Claude
Model(s): Opus 4.7
Used for: Initial code skeleton; final implementation was reviewed and tested by me.

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