Scan R etc. code for package dependencies

[gaborcsardi]

Like renv:::dependencies()

Features:

• UI about auto-scanning and the dependencies found. #420

Discovery in R code:

• methods
• xfun
• library, require
• requireNamespace, loadNamespace
• ::, :::
• pacman
• modules
• import
• box
• targets
• glue
• ggplot2
• parsnip
• testthat
• knitr
• database
• Rmd YAML header? #399

Other files:

• DESCRIPTION (?) #402
• NAMESPACE (?) #403
• bookdown #405
• pkgdown #406
• quarto #407
• renv.lock #411
• rsconnect #413
• .Rproj #414
• .qmd
• .qmd ignored chunks
• qmd: depend on rmarkdown if any r or rscript chunks
• .Rprofile #415
• .rmd
• .rmd ignored chunks
• .rmarkdown #409
• .rnw #416
• .ipynb #417

Other features:

• .gitignore
• .renvignore
• hard coded ignores:
  ignored <- c("packrat", "renv", "revdep", "vendor", if (depth) c("DESCRIPTION", "NAMESPACE"))
• Report errors?
• Find project root
• renv.config.dependencies.limit ?
• Should we pick up renv's options and env vars? IDK.
• warning about many files?
• renv.ignore knitr chunk param
• engine knitr chunk param, ignore if not r or rscript
• eval knitr chunk param, ignore if not truthy
• exercise knitr chunk param, ignore if truthy
• skip chunks whose labels end in '-display'
• make if works on a vector of files
• add root argument
• progress bar

Config options from https://rstudio.github.io/renv/reference/config.html:

• renv.config.dependency.errors
• renv.config.dependencies.limit
• renv.config.install.remotes

Docs:

• Document for deps:: as well.

[gaborcsardi]

Partially addressed by #388. Rest will be in subsequent PRs.