8d1a24da "Make virtual ~ScValidationDlg
non-inline" caused the RTTI for ScValidationDlg to only be emitted in library
scui instead of (weakly) wherever needed.  That causes UBSan to fail when it
uses the RTTI in ScValidityRefChildWin::ScValidityRefChildWin
(sc/source/ui/view/reffact.cxx, in library sc, to check that operations on
VclPtr<ScValidationDlg> pDlg indeed operate on an ScValidationDlg object).

The cleanest fix appears to be to move ScValidationDlg from scui to sc.  As
Moggi put it on IRC, "that dialog should be in sc as it is a modeless dialog; no
idea why it works for that dialog but all other modeless calc dialogs have to be
in sc to avoid linker problems."

One remaining question is whether it is save nowadays in ScCellShell::ExecuteDB
(sc/source/ui/view/cellsh2.cxx) to clean up the ScValidationDlg pointed to by
pDlg when that VclPtr<ScValidationDlg> variable goes out of scope, instead of
doing the PostUserEvent(... DelayDeleteAbstractDialog) dance that was there
before because "after end execute from !IsModalInputMode, it is safer to delay
deleting."  Lets see.

Change-Id: I3ecfd4fafc7b37b2f30e75974ece9b0a23311ef4