Support entering split screen with a shortcut and an intent

Starting a split pair by indicating (shortcut|shortcut) or
(shortcut|intent) was not properly supported, update to leverage
startIntens flow to handle shortcut info when starting a split pair.

Bug: 265919000
Test: atest WMShellUnitTests
Test: repro steps of the bug
Change-Id: I3dc639216b262249a06db86cdfb95cde773f1b48