New save format (#7050)

* New save format

Uses the Path of Exile BaseItemType.Id for the gem in gemId (as it always has been).
The skillId attribute is also kept and maps to the gems variant primary GrantedEffect.Id.
Adds a new attribute called variantId that maps to the variant of the game, eg. Arc, ArcAltX, or ArcAltY. This is to help identify which variant is used rather than relying on every gem variant having its own unique granted effect.

For the majority of gems skillId and variantId are the same, but it is not true for every case.

* Remove redundant nil check

src/Classes/SkillsTab.lua

@@ -309,16 +309,23 @@ function SkillsTabClass:LoadSkill(node, skillSetId)
 		local gemInstance = { }
 		gemInstance.nameSpec = child.attrib.nameSpec or ""
 		if child.attrib.gemId then
-			local realGemId
-			-- For now the gemId in the save file is the base gems id, so we need to add the skill id to get the real gem id
-			-- The skillId holds which variant (transfiguration) it is, eg. Arc, ArcAltX, or ArcAltY
-			-- The save format may change in the future but it is what we have for now for backward compatibility
-			if child.attrib.gemId:match("Metadata/Items/Gems/SkillGem") then
-				realGemId = "Metadata/Items/Gems/SkillGem" .. child.attrib.skillId
-			else
-				realGemId = child.attrib.gemId
+			local gemData
+			local possibleVariants = self.build.data.gemsByGameId[child.attrib.gemId]
+			if possibleVariants then
+				-- If it is a known game, try to determine which variant is used
+				if child.attrib.variantId then
+					-- New save format from 3.23 that stores the specific variation (transfiguration)
+					gemData = possibleVariants[child.attrib.variantId]
+				elseif child.attrib.skillId then
+					-- Old format relying on the uniqueness of the granted effects id
+					for _, variant in pairs(possibleVariants) do
+						if variant.grantedEffectId == child.attrib.skillId then
+							gemData = variant
+							break
+						end
+					end
+				end
 			end
-			local gemData = self.build.data.gems[realGemId]
 			if gemData then
 				gemInstance.gemId = gemData.id
 				gemInstance.skillId = gemData.grantedEffectId
@@ -447,7 +454,8 @@ function SkillsTabClass:Save(xml)
 				t_insert(node, { elem = "Gem", attrib = {
 					nameSpec = gemInstance.nameSpec,
 					skillId = gemInstance.skillId,
-					gemId = gemInstance.gemId and gemInstance.gemId:match("(Metadata/Items/Gems/SkillGem%a+)Alt[XY]"),
+					gemId = gemInstance.gemData and gemInstance.gemData.gameId,
+					variantId = gemInstance.gemData and gemInstance.gemData.variantId,
 					level = tostring(gemInstance.level),
 					quality = tostring(gemInstance.quality),
 					qualityId = gemInstance.qualityId,