Show "Arrow Symbols" instead up "UP" "DOWN" etc.

On macOS we use arrow symbols (see
xhttps://www.fileformat.info/info/unicode/char/2193/index.htm) when
formatting key bindings (e.g. in tooltips or menu entries).
This is much more compact then writing "UP", "DOWN", etc. and looks a
lot nicer.

Let's also use this on Windows and Linux.

bundles/org.eclipse.jface/src/org/eclipse/jface/bindings/keys/formatting/AbstractKeyFormatter.properties

@@ -19,10 +19,10 @@ CTRL=Ctrl
 SHIFT=Shift
 
 # Special keys
-ARROW_DOWN=Down
-ARROW_LEFT=Left
-ARROW_RIGHT=Right
-ARROW_UP=Up
+ARROW_DOWN=\u2193
+ARROW_LEFT=\u2190
+ARROW_RIGHT=\u2192
+ARROW_UP=\u2191
 BREAK=Break
 CAPS_LOCK=CapsLock
 END=End