Instead of counting entries relative to the middle of the hash table,
this switches to the absolute counter with the full index range mask.
As a result, some calculations become a bit simpler. The cache resizing
logic stays largely the same.
* src/cache/ftccache.h (FTC_NODE_TOP_FOR_HASH): Revised with new counter.
* src/cache/ftccache.c (ftc_get_top_node_for_hash): Ditto.
(ftc_cache_resize): Simplify reallocations and stop their zeroing.
(ftc_cache_init): Stop over-allocating but keep zeroing initially.
(FTC_Cache_Clear, FTC_Cache_RemoveFaceID): Updated accordingly.
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