Merge pull request #9176 from jtattermusch/runtests_refactor

.gitignore

templates/tools/run_tests/generated/configs.json.template

...ols/run_tests/generated/sources_and_headers.json.template

templates/tools/run_tests/generated/tests.json.template

tools/buildgen/generate_projects.py

tools/run_tests/artifacts/__init__.py

tools/run_tests/artifacts/artifact_targets.py

tools/run_tests/artifacts/build_artifact_csharp.bat

tools/run_tests/artifacts/build_artifact_csharp.sh

tools/run_tests/artifacts/build_artifact_node.bat

tools/run_tests/artifacts/build_artifact_node.sh

tools/run_tests/artifacts/build_artifact_php.sh

tools/run_tests/artifacts/build_artifact_protoc.bat

tools/run_tests/artifacts/build_artifact_protoc.sh

tools/run_tests/artifacts/build_artifact_python.bat

tools/run_tests/artifacts/build_artifact_python.sh

tools/run_tests/artifacts/build_artifact_ruby.sh

tools/run_tests/artifacts/build_package_node.sh

tools/run_tests/artifacts/build_package_php.sh

tools/run_tests/artifacts/build_package_python.sh