add cut/copy/paste keys

The origin of these keys are old sun keyboards.
They are getting picked up by the custom (progammable) keyboard scene
(see https://github.com/manna-harbour/miryoku for a popular layout).
Support in ghosty is quite handy because it allows to bind copy/paste in
a way that doesn't overlap with ctrl-c/ctrl-v, which can have special
bindings in some terminal applications.

include/ghostty.h

@@ -292,6 +292,11 @@ typedef enum {
   GHOSTTY_KEY_AUDIO_VOLUME_MUTE,
   GHOSTTY_KEY_AUDIO_VOLUME_UP,
   GHOSTTY_KEY_WAKE_UP,
+
+  // "Legacy, Non-standard, and Special Keys" § 3.7
+  GHOSTTY_KEY_COPY,
+  GHOSTTY_KEY_CUT,
+  GHOSTTY_KEY_PASTE,
 } ghostty_input_key_e;
 
 typedef struct {

src/apprt/gtk/key.zig

@@ -388,6 +388,10 @@ const keymap: []const RawEntry = &.{
     .{ gdk.KEY_KP_Delete, .numpad_delete },
     .{ gdk.KEY_KP_Begin, .numpad_begin },
 
+    .{ gdk.KEY_Copy, .copy },
+    .{ gdk.KEY_Cut, .cut },
+    .{ gdk.KEY_Paste, .paste },
+
     .{ gdk.KEY_Shift_L, .shift_left },
     .{ gdk.KEY_Control_L, .control_left },
     .{ gdk.KEY_Alt_L, .alt_left },

src/input/key.zig

@@ -454,6 +454,11 @@ pub const Key = enum(c_int) {
     audio_volume_up,
     wake_up,
 
+    // "Legacy, Non-standard, and Special Keys" § 3.7
+    copy,
+    cut,
+    paste,
+
     /// Converts an ASCII character to a key, if possible. This returns
     /// null if the character is unknown.
     ///
@@ -797,6 +802,9 @@ pub const Key = enum(c_int) {
             .audio_volume_up,
             .wake_up,
             .help,
+            .copy,
+            .cut,
+            .paste,
             => null,
 
             .unidentified,

src/input/keycodes.zig

@@ -130,6 +130,9 @@ const code_to_key = code_to_key: {
         .{ "PageUp", .page_up },
         .{ "Delete", .delete },
         .{ "End", .end },
+        .{ "Copy", .copy },
+        .{ "Cut", .cut },
+        .{ "Paste", .paste },
         .{ "PageDown", .page_down },
         .{ "ArrowRight", .arrow_right },
         .{ "ArrowLeft", .arrow_left },