Not sharing same task view between shortcuts

SplitScreen task shortcut was written with an expectation that only one
instance would be created at a time.

No that it's used by Accessibility, SplitScreen may be asked to provide
multiple shortcuts at a time for multiple tasks, and they share same
mTaskView.

Fixing this.

Bug: 78094307
Test: Manual
Change-Id: Ib440ca862b0677ec4a012ec9f2a225183b2c91f4