Remove region from UpvarCapture and move it to CapturedPlace

Region info is completely unnecessary for upvar capture kind computation
and is only needed to create the final upvar tuple ty. Doing so makes
creation of UpvarCapture very cheap and expose further cleanup opportunity.

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -706,10 +706,9 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         &origin_projection,
                     ) {
                         match captured_place.info.capture_kind {
-                            ty::UpvarCapture::ByRef(ty::UpvarBorrow {
-                                kind: ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
-                                ..
-                            }) => {
+                            ty::UpvarCapture::ByRef(
+                                ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
+                            ) => {
                                 capture_reason = format!("mutable borrow of `{}`", upvar);
                             }
                             ty::UpvarCapture::ByValue => {