Avoid placing shader files in `Resources` directories.

[Santarh]

依存シェーダファイルを Resources ディレクトリに置くことをやめたい。

ShaderVariantCollection に揃える。

[andreiagmu]

I'm also interested in this update, so that my builds won't compile shader variants that I don't need (I don't use MToon on my project), and to also make my build size a little smaller.

In my tests, I've used a workaround: I copied the UniVRM-related packages to my [Project Root]\Packages folder (to make the files/folders editable), then I renamed all "Resources" folders inside to "Resource". Then, it seems the VRM importer still works normally. (not sure if this breaks some other feature)

This workaround solves the extra shader variants/build size issue. But putting the UniVRM packages in that custom Packages folder makes it much less intuitive to update the packages. I prefer to install the packages via UPM (Package Manager) to easily update the packages later, but I can't edit the files/folders in that case.