typeck: adding type information to projection

This commit modifies the Place as follow:
* remove 'ty' from ProjectionKind
* add type information into to Projection
* replace 'ty' in Place with 'base_ty'
* introduce 'ty()' in `Place` to return the final type of the `Place`
* introduce `ty_before_projection()` in `Place` to return the type of
  a `Place` before i'th projection is applied

Closes rust-lang/project-rfc-2229#5

Author: Azhng

clippy_lints/src/escape.rs

@@ -150,7 +150,7 @@ impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
                     return;
                 }
 
-                if is_non_trait_box(cmt.place.ty) && !self.is_large_box(cmt.place.ty) {
+                if is_non_trait_box(cmt.place.ty()) && !self.is_large_box(cmt.place.ty()) {
                     self.set.insert(cmt.hir_id);
                 }
                 return;