Pass activity stack when saving launch params.

When setParent() is called on a task with null as a step to remove it
mParent in WindowContainer is already set to null before
onParentChanged() is called. Therefore getStack() returns null and we'll
get an NPE. Thus pass ActivityStack into it to avoid that.

Bug: 147301825
Test: NPE disappears when a task is closed.
Test: atest TestRecordTest
Change-Id: I94e81f7f22d348b73eac70edd0998be721ad2597