quarto list extensions shows internal extensions by default now

Discovered in https://github.com/quarto-dev/quarto-r/issues/301

In v1.8 it was showing like this when no extensions

❯ quarto list extensions
No extensions are installed in this directory.

in v1.9, we have added quarto engine extensions, and Typst book using extension mechanism, and now they shows always

❯ quarto list extensions
Id              Version    Contributes
julia-engine    0.1.0
orange-book     0.1.0      formats  

However, this is confusing because no information that they are internal to quarto. And before those, any internal one where not shown as extensions (hugo-md, confluence, video and other shortcode, ...).

So I would say either we need to hide them also or we could make that more clear.

One impact: In quarto R 📦 I initially use quarto list extensions to know if some extensions were installed or not... now I can't use that without encoding the default internal ones.

Ideas:

• we could mark extension 'provider' or 'origin'

❯ quarto list extensions
Id              		Version    Contributes  Origin
julia-engine    		0.1.0					internal (or quarto-cli ?)
orange-book     		0.1.0      formats      internal
quarto-ext/fontawesome  0.1.0	   filters      local (or _extensions/ ?)

• quarto list extensions shows user installed one by default, with previous table view and quarto list extensions --all shows also internal in the list

Reproduce quarto list extensions in v1.8 and v1.9, then trace the CLI's extension-listing entry point to determine how internal extensions enter the default table. Resolve whether the default should hide them or identify them, and verify the chosen behavior against the shown local-extension and no-extension cases.