[0.4.11][USER32][COMCTL32] Redraw children when the combo box is dropped down (#4138) (#5679)

port back the following commit:
0.4.15-dev-6613-g e13ebd44c6 [USER32] Pure Whitespace sync from comctl32/combo.c, no functional change
0.4.15-dev-6612-g d97313181e [USER32] Sync comctl32 combo.c code in context of CORE-17883
0.4.15-dev-3453-g ff89651ed0 [COMCTL32] Redraw children when the combo box is dropped down (#4138) CORE-17883

and tweak [USER32] combo.c a bit more even than on master, e.g. strip a few TRACEs. Possible because
unlike master we don't need to be as much in sync as possible to Wine in the older branches.
But we need to have binary size under control for the backports due to base-addresses.

Binary size:
user32.dll master    RosBEWin2.2.2 GCC8.4.0dbg               1.579.008
user32.dll 0.4.14rls RosBEWin2.1.6 GCC4.7.2dbg  1.448.448 -> 1.448.448
user32.dll 0.4.13rls RosBEWin2.1.6 GCC4.7.2dbg  1.445.376 -> 1.444.864
user32.dll 0.4.12rls RosBEWin2.1.6 GCC4.7.2dbg  1.455.616 -> 1.455.104
user32.dll 0.4.11rls RosBEWin2.1.6 GCC4.7.2dbg  1.453.056 -> 1.451.008
user32.dll 0.4.10rls RosBEWin2.1.6 GCC4.7.2dbg  1.434.624 -> 1.434.112
user32.dll 0.4. 9rls RosBEWin2.1.6 GCC4.7.2dbg  1.422.336 -> 1.421.824
user32.dll 0.4. 8rls RosBEWin2.1.6 GCC4.7.2dbg  1.421.824 -> 1.421.824
user32.dll 0.4. 7rls RosBEWin2.1.6 GCC4.7.2dbg  1.418.752 -> 1.417.216

dll/win32/comctl32/combo.c

@@ -1050,8 +1050,7 @@ static void CBDropDown( LPHEADCOMBO lphc )
 
 
    if( !(lphc->wState & CBF_NOREDRAW) )
-     RedrawWindow( lphc->self, NULL, 0, RDW_INVALIDATE |
-			   RDW_ERASE | RDW_UPDATENOW | RDW_NOCHILDREN );
+     RedrawWindow( lphc->self, NULL, 0, RDW_INVALIDATE | RDW_ERASE | RDW_UPDATENOW );
 
    EnableWindow( lphc->hWndLBox, TRUE );
    if (GetCapture() != lphc->self)