lsp-find-definition-mouse: Remember click position.

Remember click position so back-button can go back to it later.

Author: Danny Milosavljevic

Diff for: lsp-mode.el

@@ -6689,6 +6689,7 @@ REFERENCES? t when METHOD returns references."
   (let* ((ec (event-start click))
          (p1 (posn-point ec))
          (w1 (posn-window ec)))
+    (mouse-set-mark click) ; so we can go back here later
     (select-window w1)
     (goto-char p1)
     (lsp-find-definition)))