Allow closing wxAuiTabCtrl pages without switching to them.

Allow closing wxAuiTabCtrl pages without switching to them.

Clicking on the page "x" close button switched to the page before doing
anything else which was unusual as other tabbed controls don't behave like
this.

Handle clicks on the close button specially and avoid switching to the page
which is about to be closed anyhow.

Closes #14150.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71040 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775