Pokemon Emerald: Some dexsanity locations contribute evolution items

[Zunawe]

What is this fixing or adding?

Evolving pokemon isn't (currently) in-logic for dexsanity, but it's still common enough to do. But for some pokemon that evolve via item use, it can be difficult or impossible to find the relevant items.

This changes the "vanilla item" that dexsanity locations contribute if the species evolves by using those items. So with a shuffled item pool, there will always be enough evolution items to evolve all included species. And with diverse_balanced there will at least be a slightly higher concentration of evolution items.

Also technically fixes a bug where _str_to_evolution_method was missing the ITEM method, which resulted in the value being None for pokemon with evolution items. This value was never read anyway, so the bug had no effect.

How was this tested?

Generated a game with a shuffled item pool and checked the counts for a few evolution items.