Support screenshots on Non-Touch with ScreenKB as modifier (#11802)

on devices (mostly kindles) with keyboards: Alt + Shift + G
on kindle 4: ScreenKB + Menu

frontend/device/input.lua

@@ -139,7 +139,7 @@ local Input = {
             "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
             "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z",
             "Up", "Down", "Left", "Right", "Press", "Backspace", "End",
-            "Back", "Sym", "AA", "Menu", "Home", "Del",
+            "Back", "Sym", "AA", "Menu", "Home", "Del", "ScreenKB",
             "LPgBack", "RPgBack", "LPgFwd", "RPgFwd"
         },
     },
@@ -171,6 +171,7 @@ local Input = {
         Shift = false,
         Sym = false,
         Meta = false,
+        ScreenKB = false,
     },
 
     -- repeat state: