Expand touch target of split cancel button to meet a11y requirements

This CL adds a TouchDelegate to the "Cancel" button on SplitInstructionsView so that it is always at least 48dp by 48dp. I.e. if the touch target is smaller than 48dp, it expands the TouchDelegate to be at least that size.

Fixes: 323108127
Test: Manually verified that the touch target is larger
Flag: EXEMPT bugfix
Change-Id: Id14bc39660ee7767991a3b5613f1282945a2ef96