Use trust_x_header and test it (fix #195)

[jhnstrk]

Use the boolean.

Note that this changes the default behavior but makes it consistent with what the function documentation was declaring.

If we want to maintain behaviour, we may want to expose this in option in parse_form.

[Kludex]

Should we actually remove the parameter? 🤔

Do you think this makes sense @jhnstrk ?

[jhnstrk]

Should we actually remove the parameter? 🤔

Yes I think so, and also remove the X-File-Name fallback. It's not really expected for a mulitpart parser IMO.

[Kludex]

Let's drop it then 🙏