Function format_str_trim

pub fn format_str_trim(
    s: &str,
    length: Option<CharLength>,
    fail_on_len: bool,
) -> Result<String, Error>

Ensures that s has fewer than length characters, and returns a String version of it with all whitespace trimmed from the end.

The value returned is appropriate to store in Datum::String, but is not appropriate to return to clients.

This function should only fail when fail_on_len is true and length is present and exceeded.