bazel: BEP's named set of files is incomplete if an action from any output group of a set of groups fails

Let T be a target, foo-outputs and bar-outputs be output groups, foo-action and bar-action be actions in T, and foo.out and bar.out be outputs generated by foo-action and bar-action respectively.

• If we build T and request for foo-outputs, we expect foo.out to be in a NamedSetOfFiles in the BEP output. This is WAI.
• If we build T and request for foo-outputs and bar-outputs, we expect foo.out and bar.out to be in in their own NamedSetOfFiles, since they were generated by different actions foo-action and bar-action. This is WAI.
• If we build T and request for foo-outputs and bar-outputs, and bar-action fails, we expect that foo.out to still be listed in BEP. However, this is not the case and foo.out is missing, even with --keep_going.
• Additionally, if there is a target U that depends on T, U’s foo-outputs files will also be missing from the BEP.

This has caused issues with IJwB’s Java integration. See this issue for the diagnosis and a repro project. https://github.com/bazelbuild/intellij/issues/1167#issuecomment-533693212

The intuitive BEP state here is that the foo-outputs files should still be listed, regardless of failing actions requested by other output groups.