Fix Linux keyboard support for AltGr (flutter#162495)

This was previously connected to right alt, which was confusing the
keyboard handling code into generating up events for this key when it
didn't match the expected values. This key is also configurable, and
only defaults to right alt in Ubuntu/GNOME.

Fixes flutter#154053

Author: robert-ancell

dev/tools/gen_keycodes/data/gtk_logical_name_mapping.json

@@ -19,7 +19,7 @@
   "NumpadDecimal": ["KP_Period", "KP_Delete"],
   "NumpadEnter": ["KP_Enter"],
   "AltLeft": ["Alt_L"],
-  "AltRight": ["Alt_R", "ISO_Level3_Shift"],
+  "AltRight": ["Alt_R"],
   "ArrowDown": ["Down"],
   "ArrowLeft": ["Left"],
   "ArrowRight": ["Right"],

dev/tools/gen_keycodes/data/logical_key_data.g.json

@@ -1663,6 +1663,14 @@
     "names": {
       "web": [
         "AltGraph"
+      ],
+      "gtk": [
+        "ISO_Level3_Shift"
+      ]
+    },
+    "values": {
+      "gtk": [
+        65027
       ]
     }
   },
@@ -8113,8 +8121,7 @@
         "AltRight"
       ],
       "gtk": [
-        "Alt_R",
-        "ISO_Level3_Shift"
+        "Alt_R"
       ],
       "windows": [
         "RMENU"
@@ -8134,8 +8141,7 @@
         230
       ],
       "gtk": [
-        65514,
-        65027
+        65514
       ],
       "windows": [
         165

engine/src/flutter/shell/platform/linux/key_mapping.g.cc

@@ -246,7 +246,7 @@ std::map<uint64_t, uint64_t> gtk_keyval_to_logical_key_map = {
     {0x0000fd1b, 0x00100000406},  // 3270_ExSelect
     {0x0000fd1d, 0x00100000608},  // 3270_PrintScreen
     {0x0000fd1e, 0x0010000000d},  // 3270_Enter
-    {0x0000fe03, 0x00200000105},  // ISO_Level3_Shift
+    {0x0000fe03, 0x00100000103},  // ISO_Level3_Shift
     {0x0000fe08, 0x00100000709},  // ISO_Next_Group
     {0x0000fe0a, 0x0010000070a},  // ISO_Prev_Group
     {0x0000fe0c, 0x00100000707},  // ISO_First_Group

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

@@ -1753,7 +1753,7 @@ const Map<int, LogicalKeyboardKey> kGtkToLogicalKey = <int, LogicalKeyboardKey>{
   64795: LogicalKeyboardKey.exSel,
   64797: LogicalKeyboardKey.printScreen,
   64798: LogicalKeyboardKey.enter,
-  65027: LogicalKeyboardKey.altRight,
+  65027: LogicalKeyboardKey.altGraph,
   65032: LogicalKeyboardKey.groupNext,
   65034: LogicalKeyboardKey.groupPrevious,
   65036: LogicalKeyboardKey.groupFirst,