[Tech] No longer use GameManagers as singletons

[CommandMC]

Invoking a method on one of the game managers was always a little verbose: Every method took not just its own parameters, but also parameters describing the game's state (effectively that's only an AppName right now, but that may change for other store providers). Instead, there's now one Game class instance for every distinct game in the user's library

In practice, code changes in the following way:
Before:

gameManagerMap[runner].foo(appName, arg1)
gameManagerMap[runner].bar(appName)
gameManagerMap[runner].baz(appName, arg1, arg2)

After:

const game = libraryManagerMap[runner].getGame(appName)
// NOTE: `game` could potentially be passed as a parameter instead of `appName` and `runner`, making the above line unnecessary
game.foo(arg1)
game.bar()
game.baz(arg1, arg2)

As I mentioned in #4889, I plan on offloading a lot of GameInfo properties into individual methods (so there's not as much a burden on game managers to provide everything in getGameInfo all at once). Increasing the amount of method calls quickly leads to our before approach (the current code) becoming unreadable due to there being so much duplicate work.

Requires #4889

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Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)

[arielj]

I like this to remove a lot of boilerplate, I left a comment to hopefully remove more

[arielj]

I wonder if we can have a helper getGame(runner, appName), because we do this libraryManagerMap[runner].getGame(appName) a looooot

that would also help decoupling how we get the store manager throughout the app, we wouldn't need to "know" that there's a libraryManagerMap hash

[CommandMC]

I agree that we do this a lot, but I'd like to resolve this a little differently (possibly in future PRs):

• For everything in the Backend, pass around the Game instead of appName, runner
• For calls from Frontend to Backend, I was thinking that we add something like a special "type" to our IPC wrappers that, if passed from FE to BE, automatically does the equivalent of getGame(appName, runner) and passes that Game to the actual listener/handler. Call it a GameHandle maybe?