Function for_each_text_mut 

pub fn for_each_text_mut(
    content: &mut Value,
    f: &mut dyn FnMut(&mut String),
) -> usize

Apply f to every piece of text in content, in either shape, and say how many pieces it visited.

The shape is kept: a string stays a string, and an array keeps its parts in order with the ones that are not text untouched. A content of any other shape is left alone and reports 0.