bug#51648: 28.0.60; `tab-bar-close-button' and `tab-bar-new-button' should be documented in the manual

[Juri Linkov]

>>   (setq tab-bar-close-button (propertize " x" 'display (propertize "✕" 'face 
>> 'tab-bar-tab-inactive) 'close-tab t))
>>   (setq tab-bar-new-button (propertize " + " 'display (propertize "➕" 'face 
>> 'tab-bar-tab)))
>
> I thought there were some defcustom's for that, but they weren't
> easily discoverable by browsing the tab-bar customization group.  But
> if you didn't intend to let users customize those, it's up to you.

The problem is that I don't know how it's possible to customize
a string with text properties on it.