Change wxMSW-specific wxLoadUserResource() to accept standard RT_XXX types.

Resource types can be either strings for custom types or integers casted to a
TCHAR* for the standard ones. Using wxString for the resource type prevented
us from using the latter as any attempt to initialize wxString for such a
pseudo-string resulted in an immediate crash.

Change wxLoadUserResource() resource type parameter type to wxChar* to avoid
this and allow passing standard resource types, such as RT_RCDATE, to this
function directly.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72472 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775