Stardew Valley: Refactor skill progression to use new feature system

[Jouramie]

What is this fixing or adding?

While working on #3640, I realized the handling of the skill progression could greatly be improved by using the same "feature" pattern I used for a couple of xsanity settings. I had to ask myself what was going on every time there was a >= option_progressive to check if the option is progressive or progressive_with_masteries. I think it makes the code really easier to understand. This adds a great abstraction layer that could be used to extend the skill progression options. Skills were already declared in content packs, just needed to use them.

It also caught some bugs in the mod skill logic, where the vanilla rule would be used instead of the progressive rule when the option is set to progressive_with_masteries (because it was not using the >=).

How was this tested?

Unit tests

If this makes graphical changes, please attach screenshots.

N/A