When evaluating a chunk in an RMD file, the params in the yaml metadata header should be evaluated first

Is your feature request related to a problem? Please describe.

In RMD files, the yaml metadata header is ignored when evaluating chunks.

Describe the solution you'd like

The above problem can be circumvented by evaluating params <- rmarkdown::yaml_front_matter(\"$$\")$params (e.g., from a custom key mapping) beforehand. This is cumbersome though. It would be better, if the R extension would always do this before evaluating code chunks in an Rmd document.

Describe alternatives you've considered

Users can define a key map but this solution is cumbersome.

Start with the R extension's R Markdown chunk-evaluation path and the custom key-mapping workaround described in the issue. Check how rmarkdown::yaml_front_matter("$$") can provide the YAML params before a chunk runs. Done means params from the metadata header are evaluated automatically before chunk evaluation, without requiring a custom key map.