[ios] backport from 4.3-beta: expose explict module for c & cpp (#2975)

* [ios] backport from 4.3-beta: expose explict module for c & cpp

- standard user can import spine-c based api as usual
- dedicated swift/cpp user can import cpp interface with explict import and enabling cpp interp
- objective-c user can import cpp using objective-c++

* [ios] expose `SpineCppLite` so that the library user can build there own runtime based on swift package => macOS, spriteKit texture

Package.swift

@@ -18,6 +18,10 @@ let package = Package(
         .library(
             name: "Spine",
             targets: ["SpineModule"]
+        ),
+        .library(
+            name: "SpineCppLite",
+            targets: ["SpineCppLite"]
         )
     ],
     targets: [

spine-ios/Sources/SpineCppLite/include/module.modulemap

@@ -1,4 +1,13 @@
 module SpineCppLite {
+    use c
+    export c
+    explicit module cpp {
+        umbrella header "spine/spine.h"
+        requires cplusplus11
+        export *
+    }
+    explicit module c {
         header "spine-cpp-lite.h"
         export *
+    }
 }