Implement wxDirDialog:: and wxFileDialog::Create() in wxGTK.

Simply move the code from non-default constructor to Create(). This allows to
create the dialogs using 2-step creation if necessary.

Closes #14069.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70898 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -499,6 +499,7 @@ GTK:
 
 - Implement support for wxBG_STYLE_TRANSPARENT (Armel Asselin).
 - Fix wxNotebook best size calculation.
+- Implement wxDirDialog::Create() and wxFileDialog::Create() (vinayakgarg).
 
 MSW: