Limit our supported image formats.

[Ms2ger]

Prompted by #8392. We should not allow websites to use just any image format that piston happens to support. Support for any image format is a web compatibility decision that should be made as such.

[craftytrickster]

This may be an oversimplification, but could this possibly be handled in the following way?
Adding a format_not_supported method that checks the buffer against a whitelist of supported formats like:

In components/net_traits/image/base.rs , within pub fn load_from_memory

    if buffer.is_empty() {
        return None;
    }
    if (format_not_supported(buffer) {
        debug!("Image format not supported."); // should include img format in debug message
        return None;
    }

[jdm]

That sounds like the right way to do it!

[craftytrickster]

Do you mind if I take a stab at this (hopefully later today)?

[jdm]

Please do!