feat: support negative const generic parameters

* feat: support `bool` & `char` const generics

crates/hir-ty/src/interner.rs

@@ -257,12 +257,7 @@ impl chalk_ir::interner::Interner for Interner {
         c1: &Self::InternedConcreteConst,
         c2: &Self::InternedConcreteConst,
     ) -> bool {
-        match (c1, c2) {
-            (&ConstScalar::Usize(a), &ConstScalar::Usize(b)) => a == b,
-            // we were previously assuming this to be true, I'm not whether true or false on
-            // unknown values is safer.
-            (_, _) => true,
-        }
+        c1 == c2
     }
 
     fn intern_generic_arg(