NSMapTable keyed by NSTextStorage compares by text, not identity

NSMapTable.weakToStrongObjects() uses isEqual/hash for keys. NSTextStorage is an NSAttributedString, so two storages with the same text collide as one key. Its hash also changes after every edit, so lookups after mutation can miss or hit the wrong entry. For per-storage bookkeeping (edit counters, drawn-highlight caches), build the table with NSMapTable(keyOptions: [.weakMemory, .objectPointerPersonality], valueOptions: .strongMemory). Also store a weak reference to the storage next to any cached ranges, so a text view that swaps in a new storage never redraws ranges computed for the old one. The bug only showed up when a regression test forced equal edit counts on two storages with the same text.