Upgrade bazlets to latest stable-2.15

Includes the following fixes:

- Bazel: Add fixes for --incompatible_load_python_rules_from_bzl
- Bazel: Export rules_python in plugin API
- Support bazelisk or bazel in tools/eclipse/project.py
- Rework imports in project.py
- Update project.py to use argparse
- Bazel: Add fixes for --incompatible_load_java_rules_from_bzl

Change-Id: If06e157079ef79120ef02b1023987d1f98451cf1