include_runfiles with runfiles shared by multiple sources

[max-heller]

The include_runfiles behavior for pkg_files breaks down if multiple sources include the same runfile. For instance, if two sources foo and bar include a runfile blob.txt, only foo will get blob.txt in its runfiles. A warning is emitted here and the runfile is not mapped for bar:

rules_pkg/pkg/mappings.bzl

Lines 307 to 313 in 5c6aec6

	have_it = src_dest_paths_map.get(rf)
	if have_it:
	if have_it != dest_path:
	# buildifier: disable=print
	print("same source mapped to different locations", rf, have_it, dest_path)
	else:
	src_dest_paths_map[rf] = dest_path

The behavior I'd expect is that the runfile is mapping inside of foo.runfiles and bar.runfiles, either as a duplicate copy of the same file or perhaps a link to some single copy in the package.