Add into_content(self) -> D method for StyledContent<D>

[Holzhaus]

Is your feature request related to a problem? Please describe.
I have multiple StyledContent<D> object with different D. I want to convert them all to StyledContent<Cow<'a, str>>. Since content is a private field and content(&self) -> &D returns a reference, i cannot move the content out of the struct in order to convert them.

My current workaround involves cloning the value:

fn convert<'a, D: Clone + fmt::Display + Into<Cow<'a, str>>>(value: StyledContent<D>) -> StyledContent<Cow<'a, str>> {
    let style = *value.style();
    let content: D = value.content().clone();
    StyledContent::new(style, content.into())
}

Describe the solution you'd like
Add an into_content(self) -> D method that moves the content out of the struct. This would allow implementing something like this:

fn convert<'a, D: fmt::Display + Into<Cow<'a, str>>>(value: StyledContent<D>) -> StyledContent<Cow<'a, str>> {
    let style = *value.style();
    let content: D = value.into_content();
    StyledContent::new(style, content.into())
}

Describe alternatives you've considered if any

• The workaround with Clone works, but involves cloning the value unnecessarily and introduced an additional trait bound.
• Destructuring is not possible, since the fields are private.
• Of course I could also just call to_string() on the StyledContent and use these instead (and convert them into a StyledContent<Cow<'a, str>>). However, this seems hacky and I still need access to the unstyled content later, so this is not an option (because then I would need to strip the style later.

Additional context
n/a