Add and use Make targets for deps/setup

[crawfxrd]

Split the single deps.sh script into logically separate Make targets, including installing Rust in a separate script.

Note:

• CI works because GitHub runners have a thousand things installed, GNU Make included
• Submodules also aren't needed for CI as they are not used for building

[XV-02]

Are the CI checks from our github actions sufficient for testing CI functionality?

[crawfxrd]

I'm just saying I'm not bothering to explicitly install make before using Make targets because GitHub runners are guaranteed to have it already.