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 an R .qmd 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, it lets us offer these without the RStudio Keymap being on, we can offer them only in R .qmd files (right now, these also show up in Python .qmd files if you have the RStudio Keymap 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 a lot to keep them, if there is some reason I am not thinking of? 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

With the new version of the Quarto extension (updated here), you can use the keyboard shortcuts for the pipe and assignment operator in R Quarto documents but not Python ones:

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

[juliasilge]

Oh, and additionally, hopefully we can use these context keys in visual mode too eventually, related to #1805.

[juliasilge]

Kicked off a build to make Mac release builds here, to check the Quarto extension bundling:
https://github.com/posit-dev/positron-builds/actions/runs/12039692304

[jennybc]

LGTM!

In a .qmd with R chunks, inside one of those chunks, Alt+- produces <- and Cmd/Ctrl+Shift+M produces |>. With cursor inside an R chunk, the context key inspector shows quarto.document.languageId: "r".

In a .qmd with Python chunks, inside one of those chunks, Alt+- produces - and Cmd/Ctrl+Shift+M focuses PROBLEMS. With cursor inside a Python chunk, the context key inspector shows quarto.document.languageId: "python".