Add a function to look for pandoc in all known place by this package

[cderv]

Could be something like

pandoc::find_pandoc() or pandoc::look_for_pandoc() or pandoc::where_pandoc()

and then do something like

pandoc::where_pandoc(version = c("default", "system", "quarto", "rstudio"))

which would iterate through

pandoc::pandoc_bin() and setting the version.

version = "quarto" depends on

• Look for Pandoc in Quarto installed version too #48

Use cases

• FR: Auto-detect Quarto's bundled pandoc as fallback posit-dev/btw#110

[cderv]

Which is in a way what I do when the package loads

pandoc/R/pandoc-activate.R

Lines 151 to 166 in 58881e1

	on_load({
	# Set the active version to the first Pandoc binary found between:
	# * "latest" Pandoc version installed with this package
	# * "rstudio" version. Will be always found in the RStudio IDE
	# * "system" version. When one version is available on PATH
	latest_bin <- pandoc_installed_latest()
	rstudio_bin <- pandoc_which_bin("rstudio")
	system_bin <- pandoc_which_bin("system")
	if (!is.null(latest_bin)) {
	the$active_version <- latest_bin
	} else if (!is.null(rstudio_bin)) {
	the$active_version <- "rstudio"
	} else if (!is.null(system_bin)) {
	the$active_version <- "system"
	}
	})