Add a "Vanilla" tab to the settings panel.

[Icedude907]

This pull request adds a 'Vanilla' tab to sodium's settings panel, opening the vanilla game's menu screen.

While Shift+P opens the vanilla settings screen normally, this isn't immediately apparent to new users and seems like a hacky solution. It's convenient though so I've kept it.

You could argue that the button is better placed in the 'Advanced' panel, but I decided against that to keep the option easily visible for new users.

In addition, mods like Iris mixin their own tabs with custom actions, and support for this in the main project should make this process easier & less likely to cause mixin conflicts.

My implementation probably leaves much to be desired, so advice or assistance is appreciated.

[Icedude907]

If you added a button to Sodium settings, perhaps it makes sense to add one to vanilla settings as well, to get back?

Due to how the game handles submenus, hitting the escape key or Done in the vanilla video settings will send you back to the sodium settings if you came from there.

[douira]

If there is still interest in this, the branch this is targeting needs to be changed and then it could be reopened. This was only closed because branches were consolidated which resulted in PRs targeting those branches being closed automatically. However, if this PR is outdated or obsolete for other reasons it can just stay closed as it is.