Add VSCode Rust Analyzer Settings

[zicklag]

Description

Fixes errors reported by rust analyzer due to differing target and a missing cargo feature.

I'm not sure if I'm the only one who ran into this or not, so feel free to close if this shouldn't be needed for some reason!

Pre-commit steps

• Tested on QEMU and real HW Rasperry Pi.
  • Not needed if it is just a README change or similar.
• Ran ./contributor_setup.sh followed by ./devtool ready_for_publish
  • You'll need Ruby with Bundler and NPM installed locally.
  • If no Rust-related files were changed, ./devtool ready_for_publish_no_rust can be used instead (faster).
  • This step is optional, but much appreciated if done.

Note: I ran the second step above, and it generated a bunch of changes in the "diff to previous" sections, but the only change was to add a timestamp to all the diffs, which I'm assuming is just a different version of diff on my system, and is tangential to the change this PR makes, so I just didn't commit those files.

[andre-richter]

The individual tutorials have dedicated settings, e.g. https://github.com/rust-embedded/rust-raspberrypi-OS-tutorials/blob/master/17_kernel_symbols/.vscode/settings.json.

99% of the time, I am only opening a dedicated tutorial folder in VS Code, not the entire repo. But I guess it doesn't hurt to have this at the top level as well.
Could you extend your PR so that the added settings file is the same as the one from tutorial 17 linked above?

[zicklag]

Ah, that makes sense, pushed an update.

[andre-richter]

Thanks!