Copy over runfiles library from Bazel

Copybara Import from https://github.com/bazelbuild/rules_java/pull/239

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Copy over runfiles library from Bazel (#239)

The runfiles library can be maintained independently of Bazel releases and `bazel_tools` can refer to it via an alias.

Also set flags to build and test with a hermetic JDK 8 to ensure compatibility with that version.

Closes #239
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COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_java/pull/239 from fmeum:runfiles 6428328ba2bb206a281e7c02e80827f638216d96
PiperOrigin-RevId: 696993940
Change-Id: Id2ee9f4f2d15a1063c4db1e913b375ba40b8e439