Revert HasModifiers() change in behaviour, add HasAnyModifiers().

Revert HasModifiers() change in behaviour, add HasAnyModifiers().

In 2.8 wxKeyEvent::HasModifiers() returned false if (only) Shift was pressed
as it tested for Control and Alt only but when it was moved to wxKeyboardState
in r55745 it started checking for all modifiers as this made more sense now
that it was used by wxMouseEvent. However it broke existing code using it,
including in wxWidgets itself (in wxTreeCtrl), so revert it now and add
HasAnyModifiers() that does check for all modifiers, including Shift.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72251 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775