Remove duplicate method from hir::Type

I added it by mistake in #18927.

I chose to keep the method as not static, because it's more comfortable, and keep the name `add_reference()` and not `reference()`, because it is clearer and better matches `strip_reference[s]()`.

src/tools/rust-analyzer/crates/hir/src/lib.rs

@@ -4698,17 +4698,6 @@ impl Type {
         Type { env: TraitEnvironment::empty(krate), ty }
     }
 
-    pub fn reference(inner: &Type, m: Mutability) -> Type {
-        inner.derived(
-            TyKind::Ref(
-                if m.is_mut() { hir_ty::Mutability::Mut } else { hir_ty::Mutability::Not },
-                hir_ty::error_lifetime(),
-                inner.ty.clone(),
-            )
-            .intern(Interner),
-        )
-    }
-
     fn new(db: &dyn HirDatabase, lexical_env: impl HasResolver, ty: Ty) -> Type {
         let resolver = lexical_env.resolver(db.upcast());
         let environment = resolver

src/tools/rust-analyzer/crates/hir/src/term_search.rs

@@ -145,7 +145,7 @@ impl LookupTable {
                 self.data
                     .iter()
                     .find(|(t, _)| {
-                        Type::reference(t, Mutability::Shared).could_unify_with_deeply(db, ty)
+                        t.add_reference(Mutability::Shared).could_unify_with_deeply(db, ty)
                     })
                     .map(|(t, it)| {
                         it.exprs(t)

src/tools/rust-analyzer/crates/ide-assists/src/utils.rs

@@ -793,8 +793,8 @@ pub(crate) fn convert_reference_type(
 }
 
 fn could_deref_to_target(ty: &hir::Type, target: &hir::Type, db: &dyn HirDatabase) -> bool {
-    let ty_ref = hir::Type::reference(ty, hir::Mutability::Shared);
-    let target_ref = hir::Type::reference(target, hir::Mutability::Shared);
+    let ty_ref = ty.add_reference(hir::Mutability::Shared);
+    let target_ref = target.add_reference(hir::Mutability::Shared);
     ty_ref.could_coerce_to(db, &target_ref)
 }
 

src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/type_mismatch.rs

@@ -1,5 +1,5 @@
 use either::Either;
-use hir::{db::ExpandDatabase, CallableKind, ClosureStyle, HirDisplay, HirFileIdExt, InFile, Type};
+use hir::{db::ExpandDatabase, CallableKind, ClosureStyle, HirDisplay, HirFileIdExt, InFile};
 use ide_db::{
     famous_defs::FamousDefs,
     source_change::{SourceChange, SourceChangeBuilder},
@@ -88,7 +88,7 @@ fn add_reference(
     let range = ctx.sema.diagnostics_display_range((*expr_ptr).map(|it| it.into()));
 
     let (_, mutability) = d.expected.as_reference()?;
-    let actual_with_ref = Type::reference(&d.actual, mutability);
+    let actual_with_ref = d.actual.add_reference(mutability);
     if !actual_with_ref.could_coerce_to(ctx.sema.db, &d.expected) {
         return None;
     }