[libs] Add Read::take_while

[yoshuawuyts]

In #70772 I proposed adding BufRead::read_while. But as @HeroicKatora pointed out in #70772 (comment) Read::take_while would achieve many of the same benefits with fewer downsides. This would act as a counterpart to Read::take, similar to Iterator::take_while.

Examples

let mut param_name = vec![];
source
    .by_ref()
    .take_while(|b| !matches!(b, b';' | b'='))
    .read_to_end(&mut param_name)?;