Centralize some config reading function and add support for constants in mob skill db

[guilherme-gm]

Pull Request Prelude

• I have followed proper Hercules code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

The main objective of this PR is to allow the usage of constants and bitmask arrays in mob_skill_db.conf for fields that didn't support it yet.

This allows making configs a bit more readable and maybe less error prone as we have actual constants to use.

This change applies for the val* fields and Emotion, and now allows a config like: (Note: Yes, using val0 for NPC_EMOTION + Emotion doesn't make much sense, but serves as an example)

		NPC_EMOTION: {
			SkillState: "MSS_LOOT"
			SkillLevel: 1
			Rate: 2000
			Delay: 5000
			Cancelable: true
			SkillTarget: "MST_SELF"
			CastCondition: "MSC_ALWAYS"
			val0: "e_lv" //<-- Const instead of number
			val1: ["MD_CANMOVE", "MD_LOOTER"] //<-- Array with constants instead of bitmask number
			Emotion: "e_gg" //<-- Const instead of number
		}

As we already had functions to do that on itemdb (and also the same function for const in mob), I decided to centralize them in map.c (Thanks @4144 for the discussion 😄 ), this way we can use a single function and it doesn't look weird that monster is calling itemdb for no real reason.

Note: I was unsure whether I should make a script automatically update the files to use constants where possible. I am not sure if I know all the cases, but if you think it would be nice to have, I can work on a script that updates most common cases (such as slaves, emotion and mode changes)

Issues addressed:
Closes #2768