enable text-overflow property for Servo

[RichardTjokroutomo]

Enable text-overflow for Servo. Companion PR: #40526

[Loirooriol]

As said in the Servo review, since it's not handling strings or 2 values, this should alter the parser to reject these cases for Servo.

Alternatively, you can put this property behind a flag, and then in Servo make it an experimental web platform feature flag. Then it won't be enabled by default, but it will be used in tests.

[RichardTjokroutomo]

@Loirooriol I noticed earlier today that a PR on Stylo has been merged (#271), so I tried to rebase. However, I got some compilation errors.

[Loirooriol]

Since changing the struct affects things more than what I expected, maybe just do something like

        #[cfg(feature = "servo")]
        if matches!(first, TextOverflowSide::String(_)) {
            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }
        #[cfg(feature = "gecko")]
        if let Ok(second) = input.try_parse(|input| TextOverflowSide::parse(context, input)) {
            return Ok(Self {
                first,
                second,
                sides_are_logical: false,
            });
        }
        Ok(Self {
            first: TextOverflowSide::Clip,
            second: first,
            sides_are_logical: true,
        })

Or add support for strings as Nico says in servo/servo#40526 (comment)