Add onGameStateChanged and onIslandLeft events

## Events
- modApi.events.onGameStateChanged:dispatch(newGameState, oldGameState)
- modApi.events.onIslandLeft:dispatch(island)

Game States:
```
Main_Menu
Hangar
End_Game_Screen
Map
Island
Mission
Mission_Test
```

scripts/mod_loader/bootstrap/modApi.lua

@@ -101,6 +101,8 @@ t.onWindowHidden = Event()
 
 t.onMissionChanged = Event()
 t.onMissionDismissed = Event()
+t.onIslandLeft = Event()
+t.onGameStateChanged = Event()
 t.onGameVictory = Event()
 t.onSquadEnteredGame = Event()
 t.onSquadExitedGame = Event()

scripts/mod_loader/modapi/__scripts.lua

@@ -27,6 +27,7 @@ local scripts = {
 	"localization",
 	"compat",
 	"deployment",
+	"gameState",
 }
 
 local rootpath = GetParentPath(...)

scripts/mod_loader/modapi/gameState.lua

@@ -0,0 +1,97 @@
+
+GAME_STATE = {
+	MAIN_MENU = "Main_Menu",
+	HANGAR = "Hangar",
+	END_GAME_SCREEN = "End_Game_Screen",
+	MAP = "Map",
+	ISLAND = "Island",
+	MISSION = "Mission",
+	MISSION_TEST = "Mission_Test",
+}
+
+local currentGameState = GAME_STATE.MAIN_MENU
+
+function modApi:getGameState()
+	return currentGameState
+end
+
+-- Check current sector each frame. If an increment is detected,
+-- it means we have left an island. When leaving the 4th island,
+-- sector does not increase, so no event is dispatched.
+-- Event onGameStateChanged can be used to detect when the island
+-- has been fully left, when it is reflected in the save data.
+modApi.events.onFrameDrawStart:subscribe(function()
+	if not Game or not GAME then
+		return
+	end
+
+	local sector = Game:GetSector()
+
+	if GAME.currentSector == nil then
+		GAME.currentSector = sector
+	elseif GAME.currentSector < sector then
+		GAME.currentSector = sector
+
+		modApi.events.onIslandLeft:dispatch(GAME.Island)
+	end
+end)
+
+local function setGameState(gameState)
+	local oldGameState = currentGameState
+
+	if currentGameState ~= gameState then
+		currentGameState = gameState
+
+		if GAME then
+			if currentGameState == GAME_STATE.ISLAND or currentGameState == GAME_STATE.MAP then
+				-- fallbackGameState is either map or island.
+				-- When exiting a mission, or entering the game outside of a mission,
+				-- we will fall back to either of the two.
+				GAME.fallbackGameState = currentGameState
+			end
+			GAME.currentGameState = currentGameState
+		end
+
+		modApi.events.onGameStateChanged:dispatch(currentGameState, oldGameState)
+	end
+end
+
+modApi.events.onMainMenuEntered:subscribe(function()
+	setGameState(GAME_STATE.MAIN_MENU)
+end)
+
+modApi.events.onHangarEntered:subscribe(function()
+	setGameState(GAME_STATE.HANGAR)
+end)
+
+modApi.events.onGameExited:subscribe(function()
+	if not sdlext.isMainMenu() then
+		setGameState(GAME_STATE.END_GAME_SCREEN)
+	end
+end)
+
+modApi.events.onGameEntered:subscribe(function()
+	if GAME.currentGameState == nil or GAME.currentGameState == GAME_STATE.MISSION_TEST then
+		setGameState(GAME.fallbackGameState or GAME_STATE.MAP)
+	else
+		setGameState(GAME.currentGameState)
+	end
+end)
+
+modApi.events.onPreIslandSelection:subscribe(function()
+	setGameState(GAME_STATE.ISLAND)
+end)
+
+modApi.events.onIslandLeft:subscribe(function()
+	setGameState(GAME_STATE.MAP)
+end)
+
+modApi.events.onMissionChanged:subscribe(function(mission, oldMission)
+	if mission == Mission_Test then
+		setGameState(GAME_STATE.MISSION_TEST)
+	elseif mission then
+		setGameState(GAME_STATE.MISSION)
+	elseif sdlext.isGame() then
+		setGameState(GAME.fallbackGameState)
+	end
+end)