[iOS] merge shader header and disable cpp-interp in example project (#2808)

* [iOS] disable objc-interp in example project & reuse struct header inside shader

* [iOS] support sharing Shader Header on both cocoapods and SPM

Spine.podspec

@@ -18,7 +18,8 @@ Spine runtimes for iOS.
   s.platform         = :ios, '13.0'
 
   s.xcconfig = {
-    'HEADER_SEARCH_PATHS' => '"$(PODS_ROOT)/SpineCppLite/spine-cpp/spine-cpp/include" "$(PODS_ROOT)/SpineCppLite/spine-cpp/spine-cpp-lite"'
+    'HEADER_SEARCH_PATHS' => '"$(PODS_ROOT)/SpineCppLite/spine-cpp/spine-cpp/include" "$(PODS_ROOT)/SpineCppLite/spine-cpp/spine-cpp-lite"',
+    'MTL_HEADER_SEARCH_PATHS' => '"$(PODS_ROOT)/SpineShadersStructs"'
   }
 
   s.resource_bundles = {

spine-ios/Example/Spine iOS Example.xcodeproj/project.pbxproj

@@ -462,7 +462,7 @@
 				SUPPORTS_MACCATALYST = NO;
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_OBJC_BRIDGING_HEADER = "Spine iOS Example/Spine iOS Example-Bridging-Header.h";
-				SWIFT_OBJC_INTEROP_MODE = objcxx;
+				SWIFT_OBJC_INTEROP_MODE = objc;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
@@ -506,7 +506,7 @@
 				SUPPORTS_MACCATALYST = NO;
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_OBJC_BRIDGING_HEADER = "Spine iOS Example/Spine iOS Example-Bridging-Header.h";
-				SWIFT_OBJC_INTEROP_MODE = objcxx;
+				SWIFT_OBJC_INTEROP_MODE = objc;
 				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
 			};

spine-ios/Sources/Spine/Metal/SpineShaders.metal

@@ -2,27 +2,15 @@
 #include <simd/simd.h> 
 using namespace metal;
 
-typedef enum SpineVertexInputIndex {
-    SpineVertexInputIndexVertices     = 0,
-    SpineVertexInputIndexTransform    = 1,
-    SpineVertexInputIndexViewportSize = 2,
-} SpineVertexInputIndex;
-
-typedef enum SpineTextureIndex {
-    SpineTextureIndexBaseColor = 0,
-} SpineTextureIndex;
-
-typedef struct {
-    simd_float2 position;
-    simd_float4 color;
-    simd_float2 uv;
-} SpineVertex;
-
-typedef struct {
-    simd_float2 translation;
-    simd_float2 scale;
-    simd_float2 offset;
-} SpineTransform;
+#if __has_include("spine-ios/Sources/SpineShadersStructs/SpineShadersStructs.h")
+// Cocoapods Target
+    #include "spine-ios/Sources/SpineShadersStructs/SpineShadersStructs.h"
+#elif  __has_include("../../SpineShadersStructs/SpineShadersStructs.h")
+// Swift Package target
+    #include "../../SpineShadersStructs/SpineShadersStructs.h"
+#else
+    #error "Header not found. Please correct Header search path"
+#endif
 
 struct RasterizerData {
     simd_float4 position [[position]];