add spm support, bump min ios version to 12.0

apple_passkit/ios/apple_passkit.podspec

@@ -13,10 +13,11 @@ A new Flutter plugin project.
   s.license          = { :file => '../LICENSE' }
   s.author           = { 'Your Company' => 'email@example.com' }
   s.source           = { :path => '.' }
-  s.source_files = 'Classes/**/*'
+  s.source_files = 'apple_passkit/Sources/apple_passkit/**/*.swift'
   s.dependency 'Flutter'
-  s.platform = :ios, '11.0'
-  s.resource_bundles = {'apple_passkit_privacy' => ['Resources/PrivacyInfo.xcprivacy']}
+  s.platform = :ios, '12.0'
+  s.resource_bundles = {'apple_passkit_privacy' => ['apple_passkit/Sources/apple_passkit/PrivacyInfo.xcprivacy']}
+
 
   # Flutter.framework does not contain a i386 slice.
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386' }

apple_passkit/ios/apple_passkit/Package.swift

@@ -0,0 +1,24 @@
+// swift-tools-version: 5.9
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "apple_passkit",
+    platforms: [
+        .iOS("12.0"),
+    ],
+    products: [
+        .library(name: "apple-passkit", targets: ["apple_passkit"])
+    ],
+    dependencies: [],
+    targets: [
+        .target(
+            name: "apple_passkit",
+            dependencies: [],
+            resources: [
+                .process("PrivacyInfo.xcprivacy"),
+            ]
+        )
+    ]
+)