Create a top-level BUILD file that exports the `LICENSE` file.
Create a top-level BUILD file that exports the `LICENSE` file.

This is typically used in other bazel projects (e.g. tensorflow) that uses absl-py as third party packages.

Using `BUILD.bazel` to avoid potential conflicts with a `build` directory in case insensitive file systems.

Context: https://github.com/abseil/abseil-py/pull/160#issuecomment-930624267
PiperOrigin-RevId: 399963516
Change-Id: Icdac6efeff0a83c263b3d449ca1f18c24879af72

abseil/abseil-py,abseil/abseil-py