Game finders overhaul

[dartasen]

This is a spin-off of #2053, I splitted up this into several ones, so it will be easier to review. I applied the suggestions from the previous PR onto this one.

Nitrox has always defined an order in the way it searches the Subnautica installation files. This works in most cases, since users generally have only one installation of the game. However, this approach raises questions when a user has the game on both Steam & Epic.

The aim of this PR is to do away with this automatic way of doing things, by providing an API that lets you search for one or more installations of a given game (GameInfo) via flags (GameLibraries).

i.e:

IEnumerable<GameInstallation> installations = GameInstallerFinder.FindGame(GameInfo.SubnauticaZero, GameLibraries.EPIC | GameLibraries.STEAM);

var wantedInstallation = installations.Where(install => install.Origin == GameLibraries.Steam)

That will allow the launcher to display all the path, and let the user choose between them. Rather than imposing it.

What's changed

• Changed namespace to be file-scoped by default (Others are just automatic additions for available lines that were not in our .editorconfig)
• Reimplemented finders to use our GameInfo structure
• Added Microsoft finder (real game install is locked up behind OS secured folder, so for now we'll check for default path)
• Improved Steam finder to support Linux & OSX game path
• Removed CurrentDirectory finder

[Measurity]

Approved again (I messed up a unit test)

[Jannify]

LGTM CW