Massive refactoring of xenia::ui and GL swap behavior.

This seems to dramatically improve most games (especially with
--vsync=false), though it may cause swap issues with others.
New code should be easier to port, and enables elemental-forms to be
drawn for any emulator UI.

src/xenia/ui/file_picker.h

@@ -10,6 +10,7 @@
 #ifndef XENIA_UI_FILE_PICKER_H_
 #define XENIA_UI_FILE_PICKER_H_
 
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -27,6 +28,8 @@ class FilePicker {
     kDirectory = 1,
   };
 
+  static std::unique_ptr<FilePicker> Create();
+
   FilePicker()
       : mode_(Mode::kOpen),
         type_(Type::kFile),