Refactor Auto Spell and move its config to libconfig

[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

This PR was mostly part of #3230 where I have refactored Auto Spell to make easier implement the renewal rebalance. Since these rebalance PRs are taking some time for me to finish and with Keikun's suggestion of moving the config to libconfig, I decided to make this as a separate PR so we can move this part earlier.

This PR moves Auto Spell skill list to LibConfig and reworks the listing/selection logic to remove the if hard to read if chains to something more generic. This way we can implement the renewal rebalance changes with a few lines instead of a huge ugly #if/#else blocks.

To avoid as much as possible from breaking something with this rewrite, I made some sort of "unit tests" for Auto Spell to try to cover as many cases as I could. You can check the testing code in this PR in my fork: https://github.com/guilherme-gm/Hercules/pull/9/files#diff-57e0249af7272bf23858146fc95e4674d48e2ffdf89e0824333cb54e232dd56d (Only PRE-RE version of it applies to this PR, and it should work for both pre-re and re)

It is kinda hackish, but this testing PR only extracts the functions to smaller ones with the same names as in this PR so I can test it using a plugin to run as many cases as possible. The same plugin can be used in this PR and it should pass for PRE-RE and RE (if you tweak to use pre-re version of the plugin).

About the decisions on the rewrite:

• The decision of which skills to show was moved from clif to skill so skill logic stays on skill.c (as a bonus, this clif could now be used for other things, I guess)
• Cast end logic was moved out of the huge skill castend function so we can have smaller and clearer functions (and also to make it testable and pluggable)
• skill->autospell renamed to make it clear at which moment this function takes part
• Everything now uses the same list of skills, so changing the list doesn't require changing 3 different places

If you are wondering how this will cover the rebalance PR, my idea is to add a constant that may be used in SkillLevel to indicate to use half of AutoSpell level. From my tests, it should be a simple change and quite clean.

Issues addressed:
None