feat(macos): add Swift Package Manager support

lib/flutter_pty.dart

@@ -11,7 +11,11 @@ const _libName = 'flutter_pty';
 
 final DynamicLibrary _dylib = () {
   if (Platform.isMacOS || Platform.isIOS) {
-    return DynamicLibrary.open('$_libName.framework/$_libName');
+    // DynamicLibrary.process() resolves symbols from the already-loaded process
+    // image, which works for both SPM static linking and CocoaPods dynamic
+    // embedding (in the latter case the framework is already mapped into the
+    // process by the time any Dart code runs).
+    return DynamicLibrary.process();
   }
   if (Platform.isAndroid || Platform.isLinux) {
     return DynamicLibrary.open('lib$_libName.so');

macos/flutter_pty.podspec

@@ -18,7 +18,7 @@ A new Flutter FFI plugin project.
   # paths, so Classes contains a forwarder C file that relatively imports
   # `../src/*` so that the C sources can be shared among all target platforms.
   s.source           = { :path => '.' }
-  s.source_files     = 'Classes/**/*'
+  s.source_files     = 'flutter_pty/Classes/**/*'
   s.dependency 'FlutterMacOS'
 
   s.platform = :osx, '10.11'

macos/Classes/flutter_pty.c → macos/flutter_pty/Classes/flutter_pty.c

@@ -1,3 +1,3 @@
 // Relative import to be able to reuse the C sources.
 // See the comment in ../{projectName}}.podspec for more information.
-#include "../../src/flutter_pty.c"
+#include "../../../src/flutter_pty.c"

macos/flutter_pty/Package.swift

@@ -0,0 +1,19 @@
+// swift-tools-version: 5.9
+import PackageDescription
+
+let package = Package(
+    name: "flutter_pty",
+    platforms: [
+        .macOS("10.14")
+    ],
+    products: [
+        .library(name: "flutter-pty", type: .static, targets: ["flutter_pty"])
+    ],
+    targets: [
+        .target(
+            name: "flutter_pty",
+            path: "Classes",
+            publicHeadersPath: "."
+        )
+    ]
+)