Intra-doc links choose a random method if there are multiple implementations of the same generic trait

[jyn514]

This is case three from #74489.

If a type implements a trait that's generic and implemented multiple times with different generic parameters, then rustdoc generates the same link for each. For example, [String::from] resolves to https://doc.rust-lang.org/nightly/alloc/string/struct.String.html#method.from.

However, every From implementation on String has a method called from! So the browser picks a random one.

This requires two fixes:

• Handle fully-qualified syntax in intra doc links #74563, so the different implementations can be distinguished in the link
• rustdoc needs to change the #method.from it generates to distinguish the different functions in the browser

[camelid]

rustdoc needs to change the #method.from it generates to distinguish the different functions in the browser

cc #92052