[Kapu1178]

Relies on #2729

This is a big one. This PR removes IDreamList, and restructures the DreamList objects to better recycle behavior, reduce wasteful allocations, and introduce optimization routes.

Structural Changes

• DreamList is now an abstract parent class to the other list classes.
• DreamEagerList is a new abstract parent class for types that manage their contents in an eager list, like the old DreamList.
• The old DreamList is now known as a DantomList due to it's "QUIRKS", and represents user-space made list structures.
• DreamAssocList is effectively unchanged, now deriving from DreamList.
• All of the previous children of DreamList derive from the new abstract form, or DreamEagerList, if applicable.

Method Changes

• Added ToDantomList(), most of the time you're working with varying list types you will return a DantomList anyway.
• Added EnumerateLoosePairs() (needs new name, probably), a function for enumerating key-value pairs. If the given Key has no Value, it is set to DreamValue.Null.
• Added EnumerateTightPairs() (needs new name too), a function also for enumerating key-value pairs. However, this one outright excludes keys with no associated value.
• Added GetLoosePairs() and GetLooseKeys() as helpers for the above.
• Renames GetKeys() to CopyKeys(), as that's what it does.
• Added TryGetElementByKey()
• Added TryGetElementByIndex()

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