Conan: add an option that would help choosing between generating a .txt or a .py file

[sdmg15]

Hey thanks for writing this.
So it'd be nice to have such option. If this is a thing I'd love contributing by adding that.

[friendlyanon]

Seems reasonable. The reason I went with .py originally was because I wanted to make use of default_options and Conan 1 only had [requires] in the .txt version. I don't need the first one anymore and with Conan 2 there is now [test_requires] support in .txt as well.

[friendlyanon]

Unfortunately, using [layout].cmake_layout makes the generator output folder vary based on your profile. On Windows, it puts things in build/generators by default, but on *nix systems it puts things in build/<build_type>/generators. You could make this consistent across all platforms by setting tools.cmake.cmake_layout:build_folder_vars in the profile, but that's additional setup necessary on the user's end.

I'd say this is a big enough issue that I will have to turn this down and stay with the conanfile.py solution. Reverted in ff48153