Requirements for fully custom Game runtime management

[Doprez]

PR Details

The amount of internal features for Stride makes it very difficult and cumbersome to make any custom root/base features for the engine. This PR opens up a lot of those features to be accessible to any dev just referencing the released Nugets.

Now devs should be able to:

• create completely custom windows using any UI framework (Examples will be needed but probably in an external repo for a POC)
• create custom game lifetime management (hopefully for both headless and new window run Stride game)
• generally more availability to make Stride customizable without scaring users by requiring them to touch the source
• ~I need to look into it more but with the changes here to the GameBase, can we use this for separating game and window logic?~ (Nope, need to look into changing the current Gamesystems due to rendering requirements currently built into the main loop. out of scope for now, at least for this PR.)

Related Issue

https://github.com/stride3d/stride/issues/870 https://github.com/stride3d/stride/pull/1315 (Takes the initial work done by @TheKeyblader and adds a few more) https://github.com/stride3d/stride/pull/1474 https://github.com/stride3d/stride/issues/1629

Types of changes

• [ ] Docs change / refactoring / dependency upgrade
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [ ] My change requires a change to the documentation.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.
• [ ] I have built and run the editor to try this change out.