Parses a single package dependency string and extracts valid package names, excluding "R" and ignoring version constraints or comments.
extract_dependency_package_names(x)A character vector of package names extracted from the input string. The result excludes "R" and any version information.
A character string representing a package dependency specification, such as `"pkgA (>= 1.0), pkgB, R (>= 3.5.0)"`.