Rollup merge of #108828 - compiler-errors:new-solver-alias-eq-on-num-var, r=lcnr

Emit alias-eq when equating numeric var and projection

This doesn't fix everything having to do with projections and infer vars, but it does fix a common case I saw in HIR typeck.

r? `@lcnr`

compiler/rustc_middle/src/ty/mod.rs

@@ -995,7 +995,7 @@ impl<'tcx> Term<'tcx> {
 
     pub fn is_infer(&self) -> bool {
         match self.unpack() {
-            TermKind::Ty(ty) => ty.is_ty_or_numeric_infer(),
+            TermKind::Ty(ty) => ty.is_ty_var(),
             TermKind::Const(ct) => ct.is_ct_infer(),
         }
     }