Teach engine about new custom crossref

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/7653 and https://github.com/quarto-dev/quarto-cli/discussions/11394

This would work:

---
title: "Estimating associations..."
format: html
keep-md: true
crossref:
  custom: 
    - kind: float
      ref-type: supptbl
      latex-env: supptbl
      prefix: Table S
      name: Table S
      space-before-numbering: false
execute:
  echo: false
---

::: {#supptbl-info-chems}

```{r info-chems}
knitr::kable(head(cars))
```

Information about non-persistent EDCs
:::


See @supptbl-info-chems

However, OP is trying to use cell options

---
title: "Estimating associations..."
format: html
keep-md: true
crossref:
  custom: 
    - kind: float
      ref-type: supptbl
      latex-env: supptbl
      prefix: Table S
      name: Table S
      space-before-numbering: false
execute:
  echo: false
---

```{r}
#| label: supptbl-info-chems
#| tbl-cap: "Information about non-persistent EDCs"
knitr::kable(head(cars))
```

See @supptbl-info-chems

Should it work ?

Intermediate .md

::: {.cell tbl-cap='Information about non-persistent EDCs'}
::: {.cell-output-display}


| speed| dist|
|-----:|----:|
|     4|    2|
|     4|   10|
|     7|    4|
|     7|   22|
|     8|   16|
|     9|   10|


:::
:::


See @supptbl-info-chems

Currently label is not identified as tbl- or fig- so is unknown and not passed through

We could:

• Teach engine about crossref and parse it to know we should pass the labels on the .cells as for Table and Figures
• Don't filter labels, and always add a cell engine label as ID to the .cell div - may have some side effect as we don't do that by filtering out other labels.

Start by tracing how the crossref.custom configuration and the intermediate .md cell are processed, focusing on why only tbl- and fig- labels are passed through. Compare the two proposed approaches and verify the chosen behavior against the custom supptbl example. Done means the cell label is retained as an identifier and See @supptbl-info-chems resolves correctly.