[PetraAI] - Use enum-like variables instead of magic values. -- [2]
Improved readability. Easier find-and-replace.
This commit focused on:
- Worker
- TransportPlan
- Difficulty
Patch by: @JCWasmx86
Differential revision: https://code.wildfiregames.com/D4343
Refs. #6256
Comments by: @nani, @Silier, @Stan