Rollup merge of #123462 - fmease:rn-mod-sep-to-path-sep, r=nnethercote

Cleanup: Rename `ModSep` to `PathSep`

`::` is usually referred to as the *path separator* (citation needed).

The existing name `ModSep` for *module separator* is a bit misleading since it in fact separates the segments of arbitrary path segments, not only ones resolving to modules. Let me just give a shout-out to associated items (`T::Assoc`, `<Ty as Trait>::function`) and enum variants (`Option::None`).

Motivation: Reduce friction for new contributors, prevent potential confusion.

cc `@petrochenkov`
r? nnethercote or compiler

clippy_lints/src/crate_in_macro_def.rs

@@ -88,7 +88,7 @@ fn contains_unhygienic_crate_reference(tts: &TokenStream) -> Option<Span> {
         if !prev_is_dollar
             && let Some(span) = is_crate_keyword(curr)
             && let Some(next) = cursor.look_ahead(0)
-            && is_token(next, &TokenKind::ModSep)
+            && is_token(next, &TokenKind::PathSep)
         {
             return Some(span);
         }