VS Code Extension: Expose `quarto install tinytex` as a command

[cwickham]

For new users a common required step for format: pdf is installing quarto install tinytex.

It would be nice if this could be handled without sending a new user to the Terminal (e.g. in new user materials like the Get Started tutorial on quarto.org, where we generally avoid the Terminal).

I don't know if it's possible, but it would be even nicer if, when a user hits the "No TeX installation was detected" error, there could be an IDE prompt to install TinyTeX.