[DDC] Rework representation of Enums to be less redundant

[Markzipan]

Enums' representation was updated to better match the VM's hot reload semantics in 6edbfd9.

The new representation now diverges significantly from how they're represented in kernel nodes:

• Enum fields are canonicalized solely based on their name
• All non-name fields are appended to the canonicalized enum fields later (after types have been linked but after canonicalization)
• The index field is represented as a static lookup on the enclosing Enum's values field.

Our changes introduce some low hanging fruit optimization opportunities:

• index iterates through values, which is a list, using indexOf. We could make this a map for faster lookups.
• our extendEnum function effectively immediately accesses and initializes const enum fields in the const table. We should just emit these once ahead of time - likely in a separate enum handler (separate from normal consts).