Unbreak saving xref--original-window, etc

* lisp/progmodes/xref.el (xref--show-xref-buffer)
(xref--show-defs-buffer-at-bottom): Move major mode calls earlier.
So that local variable values are not lost.

lisp/progmodes/xref.el

@@ -798,8 +798,8 @@ Return an alist of the form ((FILENAME . (XREF ...)) ...)."
            (funcall fetcher)))
          (xref-alist (xref--analyze xrefs)))
     (with-current-buffer (get-buffer-create xref-buffer-name)
-      (xref--show-common-initialize xref-alist fetcher alist)
       (xref--xref-buffer-mode)
+      (xref--show-common-initialize xref-alist fetcher alist)
       (pop-to-buffer (current-buffer))
       (current-buffer))))
 
@@ -854,8 +854,8 @@ local keymap that binds `RET' to `xref-quit-and-goto-xref'."
                             (assoc-default 'display-action alist)))
      (t
       (with-current-buffer (get-buffer-create xref-buffer-name)
-        (xref--show-common-initialize (xref--analyze xrefs) fetcher alist)
         (xref--transient-buffer-mode)
+        (xref--show-common-initialize (xref--analyze xrefs) fetcher alist)
         (pop-to-buffer (current-buffer)
                        '(display-buffer-in-direction . ((direction . below))))
         (current-buffer))))))