Hide zlib and expat libs from the user of Poco libraries (replaces #4579) (#4724)

* foundation: Remove unused ucp.h

Nothing use this and it is not even included in Visual Studio project
files. Remove it so it will not confuse any more.

* foundation: Hide zlib from user

Hide zlib completly from user. This way we do not need to publish zlib.h
or zconfig.h.

As we now have two different pointer initalizing in constructor I choose
to use unique pointers so it is more obvious those are safe. I also
choose to use make_unique which default initalize z_stream_t. This makes
code more readable as we do not need to specifie every field of
z_stream_t. It really should not matter much if we initialize couple
field for nothing. If does we should add comment about that. Still
keeping _buffer without inializing as it is quite big.

* xml: Hide expat and ParserEngine from user

Hide expat completly from user. This way we do not need to publish
expat.h or expat_external.h.

I move also headers to orignal locations so diff is smaller compared to
original.

* chore(Foundation): Compression level constants

---------

Co-authored-by: Kari Argillander <kari.argillander@fidelix.com>

XML/include/Poco/SAX/SAXParser.h

@@ -20,13 +20,16 @@
 
 #include "Poco/XML/XML.h"
 #include "Poco/SAX/XMLReader.h"
-#include "Poco/XML/ParserEngine.h"
+#include "Poco/TextEncoding.h"
 
 
 namespace Poco {
 namespace XML {
 
 
+class ParserEngine;
+
+
 class XML_API SAXParser: public XMLReader
 	/// This class provides a SAX2 (Simple API for XML) interface to expat,
 	/// the XML parser toolkit.
@@ -101,7 +104,7 @@ protected:
 	void setupParse();
 
 private:
-	ParserEngine _engine;
+	ParserEngine* _engine;
 	bool _namespaces;
 	bool _namespacePrefixes;
 };