Add Settings to in-game menu, and rewrite it in C++

[swagtoy]

This PR adds settings to the pause menu.

In the past, you need to quit the current game to change settings. This is tedious, especially when on servers where you need to re-enter your password. It's also frustrating as you can't fine-tune settings such as FOV.

To do this, the lua is slowly rewritten in C++. This will probably benefit my other PR #14763, so I am going to finish this first.

Also, we can probably remove the "Sound" subsection. We could also move all the "Controls" configuration to this settings menu (which also lets us tweak controls on the main menu.. 2 birds dead with 1 stone!)

Fixes #6722, #3165, #6922, etc etc etc

How to test

1. Start a world
2. Press ESC
3. Press "settings"

(Note: As of typing this, the main menu's settings button is still the lua one)

[v-rob]

I strongly disapprove of moving GUIs to the C++ side. Formspecs were always designed to be used from Lua, and using them in C++ has always been a hack. I fully intend to move the pause menu and death screen to Lua in the future (post-formspecs).

Moreover, the formspec replacement (#14263) has zero support for usage from C++, save by serializing the GUI to a binary stream and sending it to the GUI subsystem. Moving formspecs to the C++ side is a very poor choice from a forward-looking standpoint.

[swagtoy]

I strongly disapprove of moving GUIs to the C++ side. Formspecs were always designed to be used from Lua, and using them in C++ has always been a hack. I fully intend to move the pause menu and death screen to Lua in the future (post-formspecs).

Moreover, the formspec replacement (#14263) has zero support for usage from C++, save by serializing the GUI to a binary stream and sending it to the GUI subsystem. Moving formspecs to the C++ side is a very poor choice from a forward-looking standpoint.

Initially, I wanted to do this all in Lua, however I was having trouble moving it over to the game.cpp file.

Would you like me to move them all to Lua instead, including the pause menu?

I apologize. I did not know that formspecs were discouraged from C++ usage.

[rubenwardy]

Hey, the settings GUI should stay in Lua. To show it in the mainmenu, there will need to be a secure client side Lua environment. Moving the pause menu to Lua is fine

[swagtoy]

For any future readers stumbling across this PR, please see #14785 for the Lua version 🙂