Add option to include runfiles files in the select_file search

[kpark-hrp]

Adds include_runfiles boolean argument to the select_file rule.

If set to True, runfiles files of the target is also searched for the matching subpath file.

resolves #466

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[kpark-hrp]

Hello team, @Wyverald @brandjon @tetromino

Can I get a review?

[Wyverald]

@tetromino is on leave until next year. I'm rather unfamiliar with this part of the code, so I'll leave the review to @brandjon.

[kpark-hrp]

I see. @brandjon Can you take a look at this small PR?

The default behavior doesn't change. It just adds an option.

[kpark-hrp]

@Wyverald Hey, is it possible for you to review or let @brandjon know personally?

[comius]

Skylib is one of the core libraries at least I think so. I believe it should have a higher bar to introduce new features. If there were more users requesting such a feature, I'd be more open to introducing it.

Also, PR lacks testing and support for data runfiles or symlinks that runfiles can have.

[kpark-hrp]

1. Bazel doc says avoid using data_runfiles. https://bazel.build/rules/lib/providers/DefaultInfo#data_runfiles
2. Can symlink support be added later if there is a request for it. I am currently only searching from the files parameter of the runfiles https://bazel.build/rules/lib/builtins/runfiles.html

@comius I can add a test or two for along with this PR. Would that be enough?

It would be nice to have this merged to the upstream, so I don't have to maintain a fork or patch of this skylib rule. Also, this doesn't change the default behavior of this rule, so I believe it's rather harmless.

[comius]

I have a strong argument against this change. This flattens a depset, and we should avoid that if possible. Specially in rules coming with skylib.