[PA] Refactor: rename RefCount to InSlotMetadata

To support growing demands for in-slot metadata other than BRP's
reference count, this CL renames `PartitionRefCount` to
`InSlotMetadata` and update related symbol names and comments.

Change-Id: I7dcaee714e33ebb67c4f4dd7082f39e8f1124484
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5331170
Commit-Queue: Mikihito Matsuura <[email protected]>
Reviewed-by: Bartek Nowierski <[email protected]>
Commit-Queue: Bartek Nowierski <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1269432}
NOKEYCHECK=True
GitOrigin-RevId: c986477cc62fc00827976dc655426d7649a00228
1 file changed