add sendfile method for streamsocket (#4007)

* add sendfile method for streamsocket

* add mswsock.lib to the project files and templates

* remove /DPOCO_NO_AUTOMATIC_LIBS for cmake windows build

* merge from upstream

* merge from upstream

* fix code stile
add NotImplemented exception for unsupported platforms
exculude <sys/sendfile.h> for POCO_EMSCRIPTEN, because https://
github.com/emscripten-core/emscripten/pull/16234

* add iostream include for std::cout

* fix compilation for emscripten (wrap sendfile)

Foundation/include/Poco/FileStream_POSIX.h

@@ -31,6 +31,8 @@ class Foundation_API FileStreamBuf: public BufferedBidirectionalStreamBuf
 	/// This stream buffer handles Fileio
 {
 public:
+	using NativeHandle = int;
+	
 	FileStreamBuf();
 		/// Creates a FileStreamBuf.
 
@@ -50,6 +52,12 @@ public:
 	std::streampos seekpos(std::streampos pos, std::ios::openmode mode = std::ios::in | std::ios::out);
 		/// Change to specified position, according to mode.
 
+	NativeHandle nativeHandle() const;
+		/// Returns native file descriptor handle
+	
+	Poco::UInt64 size() const;
+		/// Returns file size
+
 protected:
 	enum
 	{
@@ -61,7 +69,7 @@ protected:
 
 private:
 	std::string _path;
-	int _fd;
+	NativeHandle _fd;
 	std::streamoff _pos;
 };