Allow to customize installation directory for TinyTeX installed with quarto

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/11748

^{Originally posted by averms December 28, 2024}

Use quartoDataDir for TinyTeX (Original Title)

Description

On Linux, Quarto already follows the XDG Base Directory spec, which is very nice. It results in a clean $HOME. However, the one place it doesn't is when installing TinyTeX. It would be great if TinyTeX was also installed following the XDG Base Directory spec just like everything else. This would put it in XDG_DATA_HOME/quarto, right next to chromium.

I understand that upstream TinyTeX already has defaults and there is value in sticking to them. However, I noticed that you guys don't even use the upstream script and don't add the binaries to the user's PATH so you're already deviating from upstream.

Note about TinyTeX and its ecosystem

Default install path

• TinyTeX can be installed its install scripts, through R tinytex::install_tinytex() or through quarto install tinytex
• For now defaults installed path are aligned
• Linux: ~/.TinyTeX
• Mac: ~/Library/TinyTeX
• Windows: %APPDATA%/TinyTeX

Quarto does install by default in the same place is no existing version if found in those default place. This allows for Quarto to re-use an existing install done with R or using install script.

Custom install path

• Install script allows to customize using TINYTEX_DIR
• R install can be customized using tinytex::install_tinytex()
• For now quarto install tinytex can't be customized.

In case of customization, quarto won't be found

I believe we should at least offer a way to customize installation, either through TINYTEX_DIR env var, or through command line flag to quarto install tinytex