Simplify to vector when parsing json message for R (#3938)

So that we get vector instead of unnamed list as e.g some knitr options expect vector.

Add test for special issue with `dev` option

Author: cderv

src/resources/rmd/rmd.R

@@ -129,7 +129,7 @@
   close(stdin)
 
   # parse request and params
-  request <- jsonlite::parse_json(input)
+  request <- jsonlite::parse_json(input, simplifyVector = TRUE)
   params <- request$params
 
   # source in helper functions if we have a resourceDir

tests/docs/smoke-all/2023/01/12/knitr-options-yaml.qmd

@@ -0,0 +1,22 @@
+---
+title: "Define knitr options in YAML"
+knitr:
+  opts_chunk:
+    dev:
+      - png
+      - pdf
+      - svg
+---
+
+Issue [#3909](https://github.com/quarto-dev/quarto-cli/issues/3909) for details 
+
+```{r}
+knitr::opts_chunk$get("dev")
+```
+
+```{r}
+#| dev:
+#|   - png
+#|   - svg
+knitr::opts_current$get("dev")
+```