Shields - Dgun compatibility fix

[SethDGamre]

somewhere along the development path dguns stopped interacting with shields correctly - and they never worked consistently. This PR fixes that and adds the DGun to the bitmask that can be stopped by the extra units t3 shields.

Unchanged:

• Vanilla t2 shields don't block dgun

Changed:

• dgun projectile now sits in the same spot as it grinds against a shield, rather than jumping back arbitrary distance like before. looks better and applies damage more consistently.
• now works whether rework enabled or not consistently
• t3 shields now block dgun (but it eats through them super fast)

Other:

• GG.AddShieldDamage never worked due to being nested inside of a callin. I put it outside the callin and it now works. Ended up not using it, though.

Tested both vanilla modoptions and shield rework enabled in a crazy coop vs scavs game to check for crashes