Fix notification ordering for groups

- Only request a re-sort on behalf of notifications whose autogroup is
actually changing
- Don't allow notifications that were posted more than HANG_TIME_MS
ago be reconsidered to be intrusive
- Sort notification groups at the position of the group member
with the best authoritative rank, regardless of importance

Bug: 62895856
Bug: 63291402
Test: set AUTOGROUP_AT_COUNT to 2 in GroupHelper, and
run the AttentionManagement cts verifier test;
runtest systemui-notification

Change-Id: Ic433ca827cd01cf166b3cc11d43be639fd7a13b7