Enhance the Visual Studio installation documentation

Problem you are trying to solve

While rustup will now offer to automatically install Visual Studio, this is not the right option for all users (for licensing or other reasons). And the manual Visual Studio install continues to be a pain point for new users. Between the console install instructions and the rustup book, there is still a failure to properly communicate the requirements. Making this effort harder is that the precise steps needed can change over time as new versions of Visual Studio are released.

There are also currently multiple places where people may go looking for install instructions. These might include:

• rustup-init.exe console instructions
• https://rustup.sh
• the rustup book
• the Rust Book (either online or in print)
• https://rust-lang.org
• chat, forums, etc

It would be good if these could all link to one central page that can be updated. See also https://github.com/rust-lang/book/issues/3303.

Solution you'd like

Enhance the online docs to provide improved guidance to new users who are struggling to figure out the requirements. This would include having a walkthrough with screenshots and being clear about which Visual Studio version it applies to. The console instructions could be made more succinct (instead of "a wall of text") and link to the docs for people who need further guidance.

I would also suggest that such a walkthrough could either live at https://rustup.sh/msvc.html or redirect from there. This would allow for a shorter url which would be more convenient for consoles and printed books. Alternatively I could perhaps talk with the rust-lang.org team about setting up a redirect from that website.

### Tasks
- [ ] https://github.com/rust-lang/rustup/issues/1363
- [ ] https://github.com/rust-lang/rustup/issues/2809
- [ ] https://github.com/rust-lang/rustup/issues/2912

Start by reviewing the existing rustup-init.exe console instructions, rustup.sh, the rustup book, and the three linked tasks (#1363, #2809, and #2912). Define one central Visual Studio installation walkthrough with screenshots and version guidance, then identify which installation surfaces should link to it; the work is done when new users can find consistent, maintainable requirements and instructions.