libghostty: add cpp-vt-stream example and fix C++ header compatibility

Add a cpp-vt-stream example that verifies libghostty headers compile
cleanly in C++ mode. The example is a simplified C++ port of
c-vt-stream.

The headers used the C idiom `typedef struct Foo* Foo` for opaque
handles, which is invalid in C++ because struct tags and typedefs
share the same namespace. Fix all 12 opaque handle typedefs across the
headers to use a distinct struct tag with an Impl suffix, e.g.
`typedef struct GhosttyTerminalImpl* GhosttyTerminal`. This is a
source-compatible change for existing C consumers since the struct
tags were never referenced directly.

example/cpp-vt-stream/README.md

@@ -0,0 +1,19 @@
+# Example: VT Stream Processing in C++
+
+This contains a simple example of how to use `ghostty_terminal_vt_write`
+to parse and process VT sequences in C++. This is a simplified C++ port
+of the `c-vt-stream` example that verifies libghostty compiles in C++
+mode.
+
+> [!IMPORTANT]
+>
+> **`libghostty` is a C library.** This example is only here so our CI
+> verifies that the library can be built in used from C++ files.
+
+## Usage
+
+Run the program:
+
+```shell-session
+zig build run
+```

example/cpp-vt-stream/build.zig

@@ -0,0 +1,42 @@
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+
+    const run_step = b.step("run", "Run the app");
+
+    const exe_mod = b.createModule(.{
+        .target = target,
+        .optimize = optimize,
+    });
+    exe_mod.addCSourceFiles(.{
+        .root = b.path("src"),
+        .files = &.{"main.cpp"},
+    });
+
+    // You'll want to use a lazy dependency here so that ghostty is only
+    // downloaded if you actually need it.
+    if (b.lazyDependency("ghostty", .{
+        // Setting simd to false will force a pure static build that
+        // doesn't even require libc, but it has a significant performance
+        // penalty. If your embedding app requires libc anyway, you should
+        // always keep simd enabled.
+        // .simd = false,
+    })) |dep| {
+        exe_mod.linkLibrary(dep.artifact("ghostty-vt"));
+    }
+
+    // Exe
+    const exe = b.addExecutable(.{
+        .name = "cpp_vt_stream",
+        .root_module = exe_mod,
+    });
+    b.installArtifact(exe);
+
+    // Run
+    const run_cmd = b.addRunArtifact(exe);
+    run_cmd.step.dependOn(b.getInstallStep());
+    if (b.args) |args| run_cmd.addArgs(args);
+    run_step.dependOn(&run_cmd.step);
+}

example/cpp-vt-stream/build.zig.zon

@@ -0,0 +1,24 @@
+.{
+    .name = .cpp_vt_stream,
+    .version = "0.0.0",
+    .fingerprint = 0x112f5d044ef8c2ac,
+    .minimum_zig_version = "0.15.1",
+    .dependencies = .{
+        // Ghostty dependency. In reality, you'd probably use a URL-based
+        // dependency like the one showed (and commented out) below this one.
+        // We use a path dependency here for simplicity and to ensure our
+        // examples always test against the source they're bundled with.
+        .ghostty = .{ .path = "../../" },
+
+        // Example of what a URL-based dependency looks like:
+        // .ghostty = .{
+        //     .url = "https://github.com/ghostty-org/ghostty/archive/COMMIT.tar.gz",
+        //     .hash = "N-V-__8AAMVLTABmYkLqhZPLXnMl-KyN38R8UVYqGrxqO36s",
+        // },
+    },
+    .paths = .{
+        "build.zig",
+        "build.zig.zon",
+        "src",
+    },
+}

example/cpp-vt-stream/src/main.cpp

@@ -0,0 +1,49 @@
+#include <cassert>
+#include <cstdio>
+#include <cstring>
+#include <ghostty/vt.h>
+
+int main() {
+  // Create a terminal
+  GhosttyTerminal terminal;
+  GhosttyTerminalOptions opts = {
+    .cols = 80,
+    .rows = 24,
+    .max_scrollback = 0,
+  };
+  GhosttyResult result = ghostty_terminal_new(nullptr, &terminal, opts);
+  assert(result == GHOSTTY_SUCCESS);
+
+  // Feed VT data into the terminal
+  const char *text = "Hello from C++!\r\n";
+  ghostty_terminal_vt_write(terminal, reinterpret_cast<const uint8_t *>(text), std::strlen(text));
+
+  text = "\x1b[1;32mGreen Text\x1b[0m\r\n";
+  ghostty_terminal_vt_write(terminal, reinterpret_cast<const uint8_t *>(text), std::strlen(text));
+
+  text = "\x1b[1;1HTop-left corner\r\n";
+  ghostty_terminal_vt_write(terminal, reinterpret_cast<const uint8_t *>(text), std::strlen(text));
+
+  // Get the final terminal state as a plain string
+  GhosttyFormatterTerminalOptions fmt_opts =
+      GHOSTTY_INIT_SIZED(GhosttyFormatterTerminalOptions);
+  fmt_opts.emit = GHOSTTY_FORMATTER_FORMAT_PLAIN;
+  fmt_opts.trim = true;
+
+  GhosttyFormatter formatter;
+  result = ghostty_formatter_terminal_new(nullptr, &formatter, terminal, fmt_opts);
+  assert(result == GHOSTTY_SUCCESS);
+
+  uint8_t *buf = nullptr;
+  size_t len = 0;
+  result = ghostty_formatter_format_alloc(formatter, nullptr, &buf, &len);
+  assert(result == GHOSTTY_SUCCESS);
+
+  std::fwrite(buf, 1, len, stdout);
+  std::printf("\n");
+
+  ghostty_free(nullptr, buf, len);
+  ghostty_formatter_free(formatter);
+  ghostty_terminal_free(terminal);
+  return 0;
+}