Don't give focus to wxSearchButton when using keyboard navigation.

Don't give focus to wxSearchButton when using keyboard navigation.

The search control buttons don't show that they have focus and are not meant
to have it anyhow as they are more control decorations than real buttons and
their functionality can be activated by pressing "Enter" or "Escape" already
from the keyboard. But giving it to them made TAB behave unexpectedly and
wrongly when wxSearchCtrl had focus.

Override AcceptsFocusFromKeyboard() to return false to correct this.

See #12808.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68365 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775