Rustdoc: include crate name in links for local primitives

It makes the link easier to use in cases in which
the path of the page where it will be embedded is not
known beforehand such as when we generate impls
dynamically from `register_type_impls` method in
`main.js`

Earlier for local primitives we would generate a path
that was relative to the current page depth passed in `cx.current`
. e.g if the current page was `std::simd::prelude::Simd` the
generated path would be `../../primitive.<prim>.html`  After this
change the path will first take you to the the wesite root and add
the crate name. e.g. for `std::simd::prelude::Simd` the path now
will be `../../../std/primitive.<prim>.html`

Author: gurry

src/librustdoc/html/format.rs

@@ -879,11 +879,16 @@ fn primitive_link_fragment(
         match m.primitive_locations.get(&prim) {
             Some(&def_id) if def_id.is_local() => {
                 let len = cx.current.len();
-                let len = if len == 0 { 0 } else { len - 1 };
+                let path = if len == 0 {
+                    let cname_sym = ExternalCrate { crate_num: def_id.krate }.name(cx.tcx());
+                    format!("{cname_sym}/")
+                } else {
+                    "../".repeat(len)
+                };
                 write!(
                     f,
                     "<a class=\"primitive\" href=\"{}primitive.{}.html{fragment}\">",
-                    "../".repeat(len),
+                    path,
                     prim.as_sym()
                 )?;
                 needs_termination = true;