Don't fallback to parse usual R comments in Quarto

[cderv]

This is related to discussion in quarto-dev/quarto-cli#4306

Making this draft PR to test a scenario and discuss. This is WIP

Regarding second commit, if we don't error but just don't fallback we would get this behavior with an obscure error due to in chunk content not being parsed as option

---
title: "Example"
format: html
engine: knitr
---

```{r}
# install.packages(c("DBI", "RSQLite"))
db = DBI::dbConnect(RSQLite::SQLite(), ":memory:")
```

```{sql}
#| label: test multiqueries -5
#|  connection: db

select 1
```

processing file: test2.qmd
  |..........................................          |  80% (unnamed-chunk-2)Quitting from lines 14-18 (test2.qmd)
Error:
! The 'connection' option (DBI connection) is required for sql chunks.
Backtrace:
  1. global .main()
  2. execute(...)
  3. rmarkdown::render(...)
  4. knitr::knit(knit_input, knit_output, envir = envir, quiet = quiet)
  5. knitr:::process_file(text, output)
  8. knitr:::process_group.block(group)
  9. knitr:::call_block(x)
 10. knitr:::block_exec(params)
 13. knitr (local) engine(options)
 14. knitr:::stop2("The 'connection' option (DBI connection) is required for sql chunks.")
                                                                                                            Exécution arrêtée

[yihui]

This can be merged after xfun 0.52 is on CRAN.