Intra-doc links do not resolve for value keywords

[jyn514]

warning: `[true]` cannot be resolved, ignoring it.
 --> prim.rs:1:6
  |
1 | /// [`true`] and [`bool`]
  |      ^^^^^^ cannot be resolved, ignoring

The bug is here:

rust/src/librustdoc/passes/collect_intra_doc_links.rs

Line 1124 in fe98de2

fn is_primitive(path_str: &str, ns: Namespace) -> Option<Res> {

It only checks for types, not for values.

I opened an issue because I'm not quite sure how to fix it: Res has PrimTy but doesn't seem to have a place for keywords in the value namespace.

Originally posted by @jyn514 in #73618

[jyn514]

This looks like it might be the same issue as #63351.

[GuillaumeGomez]

I think that "true" and "false" are the two only cases for primitives where we should check for values.

[jyn514]

Closing as wontfix: #75101