Use new Quarto context keys in keyboard shortcuts

[juliasilge]

Addresses #1955 together with quarto-dev/quarto#608

The Quarto PR provides new context keys for the main language of a Quarto document (for example, R or Python) and we can consume those to provide keyboard shortcuts.

There are really only a couple of R ones that we want right now which means that there is no real change here in behavior compared to what is in the RStudio Keymap. 🙈 However, I think this is still worth getting in since we've gone to the trouble of figuring it out, because it lets us offer these without the RStudio Keymap being on and we can use this infrastructure in the future.

I did remove these from the RStudio Keymap just to clean things up, but it wouldn't hurt much to keep them, if someone can think of a reason? If we do want to remove them, we'll need to do a Quarto release and update the bundled Quarto VS Code extension version in this PR to keep these keybindings functional.

QA Notes

After installing the new version of the Quarto extension, you can use the keyboard shortcuts for the pipe and assignment operator:

• Alt+- to get you <-
• Cmd/Ctrl+Enter to get you |>

[ntluong95]

Is this the intention to press Ctrl + Enter for the pipe? I think it is going to be so confused