Add proper Pearl of Tsoatha support

[vaisest]

Description of the problem being solved:

This adds proper pearl of tsoatha support. This includes

• an item db entry
• an option to find pearls in the trader. this has a slot selector and does NOT include the base mod lines. this means that it can be misleading, but otherwise the elemental res and damage will be included in the weight.
• support for supporting item granted skills. this is done by adding a flag appliesToGrantedSkills to the on the ExtraSupport mod, and using that to allow it as an exception.
• support for supporting tree skills. this is done by adding a passive tree slot in the related gem calc code.

It seems that existing ExtraSupport code didn't have protections for duplicate support gems. I had to work around this, and there's a small caveat that they don't show up as (superseded) in the skills tab.

Steps taken to verify a working solution:

• Item tested manually
• tests added
• trader tested manually

Link to a build that showcases this PR:

Before screenshot:

After screenshot:

Note that I removed the elem dam mod here: