We've nothing like that built in for CB fields. You'd need to add the jQuery to do that using CB Auto Actions and a Code action with Method set to jQuery. We do provide a jQuery plugin with CB that provides this. See the below example auto action usage.
Global
Triggers: onBeforeUserProfileEditDisplay, onBeforeRegisterFormDisplay
Type: Code
User: Automatic
Access: Everybody
Action
Method: jQuery
Code:
Code:
$( '.cbft_textarea textarea' ).autosize();
Plugins: autosize
This likely will not work with the ajax usage.