Rename native_widget_types.h -> native_ui_types.h

This change has no functional impact on WebView2Mac. As this is purely a header file renaming operation, and the new "native_ui_types.h" file maintains full backward compatibility through #include "ui/gfx/native_widget_types.h", all original type definitions (such as NativeView, NativeWindow, NativeViewId, etc.) remain unchanged. Although the render_widget_host_view_cocoa.mm file in the remote_cocoa component, which WebView2Mac depends on, is affected, the change is limited to the header file reference path, and actual functionality remains completely consistent. The inheritance relationships, Mojo interfaces, utility class usage, and other core dependencies of WebView2Mac are not affected.