### Bug description

**distill** has also a `layout` option, and for now if the option is not correctly converted to Quarto supported one then there is an useful error 

* Content from distill without using YAML syntax
````markdown
---
title: "A small example"
format: html
page-layout: article
---

```{r setup, layout="l-body-outset"}
mtcars[,1:3] |> head()
```
````

* After conversion using `knitr::convert_chunk_header()`
````markdown
---
title: "A small example"
format: html
page-layout: article
---

```{r}
#| layout: l-body-outset
mtcars[,1:3] |> head()
```
````

in both case, we'll have this issue 
````
Error running filter C:/Users/chris/scoop/apps/quarto-prerelease/current/share/filters/layout/layout.lua:
...prerelease\current\bin\..\share\pandoc\datadir\_json.lua:167: bad 'for' initial value (number expected, got nil)
stack traceback:
	...prerelease\current\bin\..\share\pandoc\datadir\_json.lua:381: in function '_json.decode'
	...uarto-prerelease/current/share/filters/layout/layout.lua:3641: in function 'parseLayoutWidths'
	...uarto-prerelease/current/share/filters/layout/layout.lua:4274: in function 'layoutCells'
	...uarto-prerelease/current/share/filters/layout/layout.lua:4098: in function <...uarto-prerelease/current/share/filters/layout/layout.lua:4091>
ERROR: unexpected character 'l' at line 1 col 1
`````

Not so useful. 
And in the second case, YAML validation does not help to detect that. No error detected for the `layout` field in the chunk for me. 

Can we do better in the error or at least in the validation ?  

### `quarto check` Output

````
$ quarto check

[>] Checking Quarto installation......OK
      Version: 1.1.80
      Path: C:\Users\chris\scoop\apps\quarto-prerelease\current\bin\
      CodePage: unknown

[>] Checking basic markdown render....OK

[>] Checking Python 3 installation....OK
      Version: 3.9.13
      Path: C:/Users/chris/scoop/apps/pyenv/current/pyenv-win/versions/3.9.13/python3.exe
      Jupyter: 4.11.1
      Kernels: bash, julia-1.7, python3

[>] Checking Jupyter engine render....OK

(\) Checking R installation...........++ Activating rlang global_entrace

++ Setting QUARTO_PYTHON

[>] Checking R installation...........OK
      Version: 4.2.0
      Path: C:/PROGRA~1/R/R-42~1.0
      LibPaths:
        - C:/Users/chris/AppData/Local/R/win-library/4.2
        - C:/Program Files/R/R-4.2.0/library
      rmarkdown: 2.14.3

[>] Checking Knitr engine render......OK
````
cscheid
2022-08-20T13:21:25Z
cderv
enhancement yaml-validation
Future
open
Improve validation for layout to help distill conversion ? 
https://github.com/quarto-dev/quarto-cli/issues/2013