Add wxDIRCTRL_DEFAULT_STYLE for consistency with other classes.

This is, by definition, the style used as default value for the style argument
of wxDirCtrl::Create().

Closes #16525.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77530 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix harmless unused parameter warnings.

Wrap parameter in WXUNUSED() in the power resource stub functions.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77531 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775