[RESTRICT AUTOMERGE]Prevent set intent on non-leaf tasks

The root task was created with null intent, but the intent,
resize mode and other information were updated from child tasks,
which sets the split-screen-secondary root task to unresizable.

This CL is back porting from f666e494 to prevent setting the
split-screen-secondary root task to unresizable.

Bug: 230435065
Bug: 185810717
Test: atest IntentTests
      atest ActivityStarterTests
      atest TaskRecordTests
      atest testSplitscreenPortraitAppOrientationRequests
Change-Id: I856d66371ac121f681958a7129527f18a5357d0f