Map Linux AltGr to right alt. It was currently being ignored. (#73373)

Fixes https://github.com/flutter/flutter/issues/68713

dev/tools/gen_keycodes/data/key_data.json

@@ -6619,7 +6619,8 @@
         "RIGHT_ALT"
       ],
       "gtk": [
-        "Alt_R"
+        "Alt_R",
+        "ISO_Level3_Shift"
       ],
       "windows": [
         "RMENU"
@@ -6644,7 +6645,8 @@
         346
       ],
       "gtk": [
-        65514
+        65514,
+        65027
       ],
       "windows": [
         165

dev/tools/gen_keycodes/data/key_name_to_gtk_name.json

@@ -1,6 +1,6 @@
 {
   "altLeft": ["Alt_L"],
-  "altRight": ["Alt_R"],
+  "altRight": ["Alt_R", "ISO_Level3_Shift"],
   "arrowDown": ["Down", "KP_Down"],
   "arrowLeft": ["Left", "KP_Left"],
   "arrowRight": ["Right", "KP_Right"],

packages/flutter/lib/src/services/keyboard_maps.dart

@@ -1664,6 +1664,7 @@ const Map<int, LogicalKeyboardKey> kGtkToLogicalKey = <int, LogicalKeyboardKey>{
   65508: LogicalKeyboardKey.controlRight,
   65506: LogicalKeyboardKey.shiftRight,
   65514: LogicalKeyboardKey.altRight,
+  65027: LogicalKeyboardKey.altRight,
   65512: LogicalKeyboardKey.metaRight,
   269025026: LogicalKeyboardKey.brightnessUp,
   269025027: LogicalKeyboardKey.brightnessDown,