[stdlib] Clean up Set and Dictionary

- Use _HashTable to unify low-level hashing operations across Set and Dictionary.
- Store the capacity directly inside the storage header. This allows the maximum load factor to be controlled by non-inlinable code.
- Introduce a dedicated class for the empty singleton.
- Add _BridgingHashBuffer, a standalone flat hash buffer for use in deferred bridging. Use it to eliminate the need to support non-hashable storage/wrapper variants and to improve memory use in cases where Key or Value are verbatim bridged.
- Eliminate the “TypedNative*Storage” class and _NativeSet/_NativeDictionary’s support for non-hashable keys.
- Rename storage classes as follows:

_RawNativeSetStorage ⟹ _RawSetStorage
_RawNativeDictionaryStorage ⟹ _RawDictionaryStorage
_TypedNativeSetStorage ⟹ (removed)
_TypedNativeDictionaryStorage ⟹ (removed)
_HashableTypedNativeSetStorage ⟹ _SetStorage
_HashableTypedNativeDictionaryStorage ⟹ _DictionaryStorage

The new names make it obvious which ivar layout is in use.

Author: lorentey

stdlib/public/SwiftShims/GlobalObjects.h

@@ -40,36 +40,33 @@ struct _SwiftEmptyArrayStorage {
 SWIFT_RUNTIME_STDLIB_API
 struct _SwiftEmptyArrayStorage _swiftEmptyArrayStorage;
 
-struct _SwiftUnsafeBitMap {
-  __swift_uintptr_t *values;
-  __swift_intptr_t bitCount;
-};
-
 struct _SwiftDictionaryBodyStorage {
-  __swift_intptr_t capacity;
   __swift_intptr_t count;
-  struct _SwiftUnsafeBitMap initializedEntries;
-  void *keys;
-  void *values;
+  __swift_intptr_t capacity;
+  __swift_intptr_t scale;
+  __swift_uint64_t seed;
+  void *rawKeys;
+  void *rawValues;
 };
 
 struct _SwiftSetBodyStorage {
-  __swift_intptr_t capacity;
   __swift_intptr_t count;
-  struct _SwiftUnsafeBitMap initializedEntries;
-  void *keys;
+  __swift_intptr_t capacity;
+  __swift_intptr_t scale;
+  __swift_uint64_t seed;
+  void *rawElements;
 };
 
 struct _SwiftEmptyDictionarySingleton {
   struct HeapObject header;
   struct _SwiftDictionaryBodyStorage body;
-  __swift_uintptr_t entries;
+  __swift_uint64_t metadata;
 };
 
 struct _SwiftEmptySetSingleton {
   struct HeapObject header;
   struct _SwiftSetBodyStorage body;
-  __swift_uintptr_t entries;
+  __swift_uint64_t metadata;
 };
 
 SWIFT_RUNTIME_STDLIB_API