Expose the remote JDK's legal/ directory from the generated BUILD file #390

The BUILD file that rules_java generates for remote JDK repositories (toolchains/jdk_build_file.bzl, JDK_BUILD_TEMPLATE) exposes the runtime's bin, conf, lib, include and jmods through filegroups, and exports only WORKSPACE and BUILD.bazel. The archive's legal/ directory is downloaded but not reachable from any target.

Projects that package the remote JDK into a container image and redistribute it need those files: OpenJDK is GPL-2.0 with the Classpath Exception and bundles third-party components whose licenses require their notices to accompany copies. Today the only way to get them is to patch JDK_BUILD_TEMPLATE.

Would you accept exporting them, for example a legal filegroup (glob(["legal/**"], allow_empty = True)) or adding legal/** to exports_files? Observed with rules_java 9.3.0 and remotejdk21_linux. Happy to send a PR.