BAZEL_STABLE_STATUS_FILE and BAZEL_VOLATILE_STATUS_FILE should contain absolute paths

Currently `BAZEL_STABLE_STATUS_FILE` and `BAZEL_VOLTAILE_STATUS_FILE` are set in the env for stamp-aware build actions like `run_binary`. The trouble, these are set to relative paths from the execroot e.g. `bazel-out/volatile-status.txt`, which is not so helpful if..

* Using rules_js, where build actions run in the BINDIR and not the execroot
* Using rules with custom `chdir` settings

To eliminate the need for any path foo, it would be more helpful if these provided absolute filepaths that could be read as-is regardless of context.

Start by locating where BAZEL_STABLE_STATUS_FILE and BAZEL_VOLATILE_STATUS_FILE are added to the environment for stamp-aware actions such as run_binary. Check how paths are resolved relative to the execroot, BINDIR, and custom chdir settings; done means both variables contain absolute paths that actions can read unchanged from any working directory.

Written by the indexing model from the issue text.