fix(slides): negative number indicates position starting at end (#10997)
fix(slides): negative number indicates position starting at end (#10997)

* fix(slides): negative number indicates position starting at end

* refactor(slides): use var instead of let

alan-agius4/ionic,driftyco/ionic,TillaTheHun0/ionic,driftyco/ionic,driftyco/ionic,alan-agius4/ionic,alan-agius4/ionic,TillaTheHun0/ionic,TillaTheHun0/ionic,TillaTheHun0/ionic,alan-agius4/ionic,alan-agius4/ionic,alan-agius4/ionic,driftyco/ionic,driftyco/ionic