New icon for Linux GTK app that aligns with the Gnome HIG

This adds a new icon for the GTK-based application that adheres (mostly)
to the Gnome Human Interface Guidelines (HIG). The icon is designed to
fit in better with other Gnome applications. 

While there isn't a single standard "native" style amongst Linux
applications, I believe this better fits the general Linux desktop
ecosystem over our macOS icon.

The icon itself is undeniably Ghostty. The core design language is the
same and I don't think ayone will mistake it for anything else. I wanted
to keep the brand the same, but making it fit in better aligns with
Ghostty's goal of being "platform native".

src/apprt/gtk-ng/build/gresource.zig

@@ -63,8 +63,8 @@ pub const file_inputs = deps: {
     var deps: [total][]const u8 = undefined;
     var index: usize = 0;
     for (icon_sizes) |size| {
-        deps[index] = std.fmt.comptimePrint("images/icons/icon_{d}.png", .{size});
-        deps[index + 1] = std.fmt.comptimePrint("images/icons/icon_{d}@2x.png", .{size});
+        deps[index] = std.fmt.comptimePrint("images/gnome/{d}.png", .{size});
+        deps[index + 1] = std.fmt.comptimePrint("images/gnome/{d}.png", .{size * 2});
         index += 2;
     }
     for (blueprints) |bp| {
@@ -162,7 +162,7 @@ fn genIcons(writer: anytype) !void {
         // 1x
         {
             const alias = std.fmt.comptimePrint("{d}x{d}", .{ size, size });
-            const source = std.fmt.comptimePrint("images/icons/icon_{d}.png", .{size});
+            const source = std.fmt.comptimePrint("images/gnome/{d}.png", .{size});
             try cwd.access(source, .{});
             try writer.print(
                 \\    <file alias="{s}/apps/{s}.png">{s}</file>
@@ -175,7 +175,7 @@ fn genIcons(writer: anytype) !void {
         // 2x
         {
             const alias = std.fmt.comptimePrint("{d}x{d}@2", .{ size, size });
-            const source = std.fmt.comptimePrint("images/icons/icon_{d}@2x.png", .{size});
+            const source = std.fmt.comptimePrint("images/gnome/{d}.png", .{size * 2});
             try cwd.access(source, .{});
             try writer.print(
                 \\    <file alias="{s}/apps/{s}.png">{s}</file>

src/apprt/gtk/gresource.zig

@@ -17,7 +17,7 @@ const icons = [_]struct {
     },
     .{
         .alias = "16x16@2",
-        .source = "16@2x",
+        .source = "32",
     },
     .{
         .alias = "32x32",
@@ -25,7 +25,7 @@ const icons = [_]struct {
     },
     .{
         .alias = "32x32@2",
-        .source = "32@2x",
+        .source = "64",
     },
     .{
         .alias = "128x128",
@@ -33,7 +33,7 @@ const icons = [_]struct {
     },
     .{
         .alias = "128x128@2",
-        .source = "128@2x",
+        .source = "256",
     },
     .{
         .alias = "256x256",
@@ -41,7 +41,7 @@ const icons = [_]struct {
     },
     .{
         .alias = "256x256@2",
-        .source = "256@2x",
+        .source = "512",
     },
     .{
         .alias = "512x512",
@@ -116,7 +116,7 @@ pub fn main() !void {
     );
     for (icons) |icon| {
         try writer.print(
-            "    <file alias=\"{s}/apps/com.mitchellh.ghostty.png\">images/icons/icon_{s}.png</file>\n",
+            "    <file alias=\"{s}/apps/com.mitchellh.ghostty.png\">images/gnome/{s}.png</file>\n",
             .{ icon.alias, icon.source },
         );
     }
@@ -153,7 +153,7 @@ pub const dependencies = deps: {
         index += 1;
     }
     for (icons) |icon| {
-        deps[index] = std.fmt.comptimePrint("images/icons/icon_{s}.png", .{icon.source});
+        deps[index] = std.fmt.comptimePrint("images/gnome/{s}.png", .{icon.source});
         index += 1;
     }
     for (blueprint_files) |blueprint_file| {

src/build/GhosttyResources.zig

@@ -360,47 +360,47 @@ fn addLinuxAppResources(
     // Various icons that our application can use, including the icon
     // that will be used for the desktop.
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_16.png"),
+        b.path("images/gnome/16.png"),
         "share/icons/hicolor/16x16/apps/com.mitchellh.ghostty.png",
     ).step);
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_32.png"),
+        b.path("images/gnome/32.png"),
         "share/icons/hicolor/32x32/apps/com.mitchellh.ghostty.png",
     ).step);
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_128.png"),
+        b.path("images/gnome/128.png"),
         "share/icons/hicolor/128x128/apps/com.mitchellh.ghostty.png",
     ).step);
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_256.png"),
+        b.path("images/gnome/256.png"),
         "share/icons/hicolor/256x256/apps/com.mitchellh.ghostty.png",
     ).step);
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_512.png"),
+        b.path("images/gnome/512.png"),
         "share/icons/hicolor/512x512/apps/com.mitchellh.ghostty.png",
     ).step);
     // Flatpaks only support icons up to 512x512.
     if (!cfg.flatpak) {
         try steps.append(&b.addInstallFile(
-            b.path("images/icons/icon_1024.png"),
+            b.path("images/gnome/1024.png"),
             "share/icons/hicolor/1024x1024/apps/com.mitchellh.ghostty.png",
         ).step);
     }
 
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_16@2x.png"),
+        b.path("images/gnome/32.png"),
         "share/icons/hicolor/16x16@2/apps/com.mitchellh.ghostty.png",
     ).step);
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_32@2x.png"),
+        b.path("images/gnome/64.png"),
         "share/icons/hicolor/32x32@2/apps/com.mitchellh.ghostty.png",
     ).step);
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_128@2x.png"),
+        b.path("images/gnome/256.png"),
         "share/icons/hicolor/128x128@2/apps/com.mitchellh.ghostty.png",
     ).step);
     try steps.append(&b.addInstallFile(
-        b.path("images/icons/icon_256@2x.png"),
+        b.path("images/gnome/512.png"),
         "share/icons/hicolor/256x256@2/apps/com.mitchellh.ghostty.png",
     ).step);
 }