Include ANTLR license with the build JAR in Hydra 1.4 sdists

Summary

Hydra 1.4's source distribution includes build_helpers/bin/antlr-4.11.1-complete.jar, but does not include the repository's existing ATTRIBUTION/LICENSE-antlr4 file.

Hydra 1.4 does not carry its own copy of the ANTLR Python runtime: it depends on OmegaConf 2.4 and the generated parser imports omegaconf.vendor.antlr4. Runtime attribution therefore belongs to the OmegaConf distribution. This issue is specifically about the ANTLR generator JAR redistributed in Hydra's sdist.

Proposed fix

• Include ATTRIBUTION/LICENSE-antlr4 in the sdist alongside the JAR.
• Declare it as a distribution license file using the packaging configuration supported by the project.
• Add an artifact-level check that verifies:
  • an sdist containing the ANTLR JAR also contains the ANTLR license;
  • the wheel does not accidentally contain the build-only JAR.

Alternatively, if building from an sdist no longer needs the JAR, exclude the JAR from the sdist.