Don't (ab)use `TyKind::Error` when not planning to emit error

[mark-i-m]

cc #70551 @eddyb

Currently, it appears we are misusing TyKind::Error (and Const::Error) in these places, which we should refactor:

• fixed by Fix abuses of tykind::err #70870

  rust/src/librustc_typeck/check/wfcheck.rs

  Line 710 in 6dee5f1

  fcx.tcx.types.err.into()

• fixed by Fix abuses of tykind::err #70870

  rust/src/librustc_typeck/check/wfcheck.rs

  Line 715 in 6dee5f1

  fcx.tcx.consts.err.into()

• fixed by Fix abuses of tykind::err #70870

  rust/src/librustc_typeck/lib.rs

  Line 383 in 6dee5f1

  tcx.types.err,

• fixed by Fix abuses of tykind::err #70870

  rust/src/librustc_typeck/variance/constraints.rs

  Line 319 in 6dee5f1

  poly_trait_ref.with_self_ty(self.tcx(), self.tcx().types.err);

• fixed by De-abuse TyKind::Error in pattern type checking #70932

  rust/src/librustc_typeck/check/pat.rs

  Lines 1428 to 1435 in 42abbd8

  	return (self.tcx.types.err, updated_arr_ty);
  	} else {
  	// We have a variable-length pattern and don't know the array length.
  	// This happens if we have e.g.,
  	// `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
  	self.error_scrutinee_unfixed_length(span);
  	}
  	(self.tcx.types.err, arr_ty)

• fixed by Use trait_object_dummy_self instead of err #71938

  rust/src/librustc_typeck/check/closure.rs

  Line 180 in 93dc97a

  let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);

• fixed by ty/walk: iterate GenericArgs instead of Tys. #70164

  rust/src/librustc_trait_selection/traits/select.rs

  Line 3079 in 6dee5f1

  .map(|(i, &k)| if ty_params.contains(i) { tcx.types.err.into() } else { k });

• fixed by De-abuse TyKind::Error in exhaustiveness checking #71930

  rust/src/librustc_mir_build/hair/pattern/_match.rs

  Line 900 in 9fed360

  (false, ..) => cx.tcx.types.err,