#8907: The image caption should be controlled using the toolbar button

[oleq]

Suggested merge commit message (convention)

Other (image): The image caption should be controlled using the toolbar button and a command for better integration with image styles. Closes #8907.

---

Additional information

BREAKING CHANGE (image): The caption will no longer show up automatically when a caption-less image gets selected. To show the caption, use the button in the image toolbar or execute the ToggleImageCaptionCommand command (editor.execute( 'toggleImageCaption' )).

[oleq]

TBH, the longer I use this feature with auto-focus when the caption shows up, the more I hate it. There are so many things happening at once (the toolbar disappears, image styles change, the caption appears, the caret moves). Also, on top of this, if we go this way, the user will (almost) never get the chance to read the placeholder and could be puzzled by this empty box under the image. 

WDYT @magda-chrzescian? (it's related to #8907 (comment))

[magda-chrzescian]

@oleq I usually trust the impressions of using something and well, if it feels wrong, maybe we should just change it. But I'm still afraid that we will put the needs of the inexperienced user before the needs of someone who already got used to the editor and just wants to get things done quickly.

It would be nice to see this feature working with the image styles before making the final decision.