[Permission Hub Refactor] Fix stale "Today" "Yesterday" on the permission usage details page

MIDNIGHT_TODAY and MIDNIGHT_YESTERDAY was cached as static value in the code. So it didn't update its value when
time passes which caused incorrect showing of "Today" and "Yesterday" on the timeline page. Moving it to local
variable will make the value update everytime the code runs.

Bug: 277111889
Test: Manual, atest CtsPermission3TestCases:PermissionHistoryTest
Change-Id: I8bc8029ddf0b0cc8dd906527f88e6285a03fc554