Make core/ includes absolute, remove subfolders from include path

This allows more consistency in the manner we include core headers,
where previously there would be a mix of absolute, relative and
include path-dependent includes.

platform/javascript/http_client_javascript.cpp

@@ -28,8 +28,8 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
+#include "core/io/http_client.h"
 #include "http_request.h"
-#include "io/http_client.h"
 
 Error HTTPClient::connect_to_host(const String &p_host, int p_port, bool p_ssl, bool p_verify_host) {