Rustdoc should preserve order of item declaration by default.

[nixpulvis]

I'm trying to write code in a specific order for the proposes of reading, and the fact that it sorts them by default alphabetically is not what I want.

At least make it an option, what the default it might be an argument.

[apasel422]

Sort of a duplicate of #8552.

[QuietMisdreavus]

Current status: Thanks to #46787 there is a --sort-modules-by-appearance flag that will leave items on module pages in declaration order. The flag is still unstable, but it exists.

[Dylan-DPC]

Closing this as it is implemented by #46787