Change SplitInstructionsView cancel from X to "Cancel"

* Styling (accent color) is still a TODO,
just made it bold for now.

Flag: ACONFIG com.android.wm.shell.enable_split_contextual DEVELOPMENT
Bug: 295983387
Test: Tested w/ flag on and off, cancel doesn't show
with flag off

Change-Id: Id5214a86abbe0cf095e32f6f75522ea51d6b1f3c
5 files changed