Fix confusing behavior with onFocus/onFocusLost

[Geokureli]

Issue started here: #3271
There seems to be a lot of things going wrong here:

• Calling sound.onFocus when the game has focus, assumes all paused sounds should be resumed
• FlxGame.onFocus only checks if it already has focus on flash, but should probably check on all targets (?)
• I'm not sure why closing the debug menu triggered a focus event, when focus isn't lost. I wonder if a certain menu takes focus, I know selecting the console pauses the game, but this doesn't seem to take focus, and doesn't require onFocus to unpause the game when closing the debug menu

Things might be fine with 3271, but I want to look into this later