Rewrite of the files and folders section

[ferafiks]

Motivation

The files and folders section is quite outdated and is lacking a lot of useful information. On top of that, the name of the section is quite misleading, implying to be about IO operations.

Additionally, there are other very minor sections that could be merged with files and folders into one, removing clutter from the sidebar.

Description

This PR:

1. Merges "files and folders", "Nuget" and "Extensibility" sections into one, called "Project"
2. Rewrites all pages pages under those sections
3. Replaces outdated information
4. Adds a new sub-section "packages" that goes into detail how they work and how to work with them
5. All pages now have instructions for Visual Studio and manual/command line

Highlights

New sub-section "Building the game" that goes into detail how to setup, build and cleanup the game, providing a guide on how to make the publish directory look like this out of the box

New section "Packages" that includes information on how a C# solution works, how to create and configure additional packages and how dependencies work

New instructions for using Nuget packages and completely redone instructions on how to create add assets and publish them.

TODO

• Rewrite existing pages under Files and folders
• Add package pages
• Rewrite "distribute a game"
• Rewrite existing pages under Nuget
• Rewrite existing pages under Extensibility
• Rewrite "distribute a game"
• Create visualizations

[ferafiks]

Aside from missing visualizations, the PR is ready for review.

Also note, I originally planned to rewrite the engine asset pages and place them in the new section, but there are already a lot of changes and I could just do that in another PR.

A few points of discussion:

• Should the section have a different name? The section includes information about how a Stride project works and how to work with it, but maybe someone has a better suggestion.
• Is there anything else that should be included in the Building the game > Setup page? I think I included the most important settings, but maybe there is something that should also go there.
• Should the Building the game > Build file structure be different? The page describes the structure for Windows/Mac/Linux builds. I'm not sure about Android nor iOS and I'm not really keen on having to figure out how to make a Stride game run on my phone at the moment.