Rename Stack to Task related terms (1/n)

No logical changes, just renaming which includes
- STACK_VISIBILITY to TASK_VISIBILITY
- ReparentMoveStackMode to ReparentMoveRootTaskMode
- TAG_STACK to TAG_ROOTTASK
- DEBUG_STACK to DEBUG_ROOTTASK
- MATCH_ATTACHED_TASK_ONLY to MATCH_ATTACHED_TASK_ONLY

Bug: 157876447
Test: presubmit
Change-Id: I367faf32b0729580a1a213ac9631e5ff0aaf6636