move Filament headers to own directory under iOS/macOS

macos/include/backend/platforms/OpenGLPlatform.h

@@ -288,6 +288,12 @@ public:
      * @see terminate()
      */
     virtual void createContext(bool shared);
+
+    /**
+     * Detach and destroy the current context if any and releases all resources associated to
+     * this thread.
+     */
+    virtual void releaseContext() noexcept;
 };
 
 } // namespace filament

macos/include/backend/platforms/PlatformEGL.h

@@ -40,6 +40,7 @@ public:
     PlatformEGL() noexcept;
     bool isExtraContextSupported() const noexcept override;
     void createContext(bool shared) override;
+    void releaseContext() noexcept override;
 
 protected:
 
@@ -139,6 +140,7 @@ protected:
             bool KHR_create_context = false;
             bool KHR_gl_colorspace = false;
             bool KHR_no_config_context = false;
+            bool KHR_surfaceless_context = false;
         } egl;
     } ext;