Add a button to show all content, if the zoom allows it. (#1406)

* add zoom center action button

* enhance zoom calculation and scroll to center

* add zoom out and center button

* filter deleted elements

* improve complexity

* add key shortcut

* calculate zoom value

* don't render zoomCenter action

* offset from top to account for shape menu

* change shortcut & add to shortcut dialog

* decrease offset

* revert offset

* change hotkey & description

* rename to zoomToFit

* change shortcut label & position

Co-authored-by: dwelle <luzar.david@gmail.com>

src/locales/en.json

@@ -150,7 +150,8 @@
     "howto": "Follow our guides",
     "github": "Found an issue? Submit",
     "textNewLine": "Add new line (text)",
-    "textFinish": "Finish editing (text)"
+    "textFinish": "Finish editing (text)",
+    "zoomToFit": "Zoom to fit all elements"
   },
   "encrypted": {
     "tooltip": "Your drawings are end-to-end encrypted so Excalidraw's servers will never see them.\nClick the icon to learn more..."