Fixes#32615
This was tricky and I don't really know what was causing the issue,
but looks like the patch doesn't break the other dialogs (mainly
vector layer properties) that were affected by #31449.
Fixes also an unreported issue with OGR source select inner dialog
not being painted when opening the source manager dialog.
This is an attempt to fix the layout of the vector
layer dialog to fit in the unified dialog layout.
The optiomal solution would probably involve
a complete refactoring of the vector layer dialog
to use a stacked widget.