Fragile code in loose `LuaUI/main.lua` causes LuaUI crash

https://github.com/beyond-all-reason/RecoilEngine/blob/b081fd2a1ba0b982f00d09ae752bffb2bb58f7b4/cont/LuaUI/main.lua#L16-L17

These two lines expect specific files inside `VFS.ZIP`, so any game using that `main.lua` will just have its LuaUI crash at init.

Revert the inclusion of `utils.lua` to its previous mode (was left nil, I assume that's either RAW_FIRST or just RAW) since it worked before.

rml_setup is new so there's a choice between guarding the `VFS.Include` line with some sort of `if VFS.FileExists(..., VFS.ZIP)`, or putting rml_setup into basecontent so it's in `VFS.ZIP`. (The third option is to change the include line from ZIP to RAW(_FIRST), but I dislike it for #1483 reasons).

Start at cont/LuaUI/main.lua lines 16–17 and inspect how the two VFS.Include calls resolve files in VFS.ZIP. Compare utils.lua with its previous inclusion mode, then review the available handling for the new rml_setup file. Done means LuaUI initialization no longer crashes for games missing these files, with the chosen behavior covered by an appropriate check or content update.

Written by the indexing model from the issue text.