Fix fixed-width progress columns in generic wxDataViewCtrl.

Both native wxDVC implementations grow the progress column, the generic
one didn't.  This change fixes it and _seems_ not to break other things.
As a consequence, progress columns no longer have a 40px minimal width,
but that should be OK.

Fixes #15745.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75346 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/datavgen.cpp

@@ -1195,7 +1195,11 @@ wxDataViewProgressRenderer::Render(wxRect rect, wxDC *dc, int WXUNUSED(state))
 
 wxSize wxDataViewProgressRenderer::GetSize() const
 {
-    return wxSize(40,12);
+    // Return -1 width because a progress bar fits any width; unlike most
+    // renderers, it doesn't have a "good" width for the content. This makes it
+    // grow to the whole column, which is pretty much always the desired
+    // behaviour. Keep the height fixed so that the progress bar isn't too fat.
+    return wxSize(-1, 12);
 }
 
 // ---------------------------------------------------------