Add debug logging to PerDisplayStore

This commit adds log statements to the PerDisplayStore to track the creation and removal of per-display instances.

Specifically, it adds:
- A debug log when a new instance is created for a display.
- A verbose log when an instance is removed for a display.

This will aid in debugging issues related to display management and instance lifecycle.

Bug: 440321599
Test: check logs
Flag: NONE - adding logs
Change-Id: I1a8c27c608c40db2bb698fd3f4cb3aba847554a8