This commit upgrades gRPC to protobuf v25.0 and makes some fixes to
account for upb changes. One major change is that upb has been merged
into the protobuf repo, so we can now drop the separate `@upb`
dependency. Another is that `.upb.c` files no longer exist and there are
new `.upb_minitable.h` and `.upb_minitable.c` files. The longer
filenames exceeded a Windows restriction, so to work around that I
renamed the `upb-generated` directory to just `upb-gen`, and likewise
for `upbdefs-generated`.
* Use latest pylint in Python 3.7 (they dropped support for PY2)
* Make latest pylint happy
* Forced to upgrade to shellcheck 0.4.4
* Make shellcheck 0.4.4 happy
* Adopt reviewers' advice to reduce global disabled rules
The source code is moved from src/python to
src/python/src. A setup.py is added at
src/python. The build_python.sh and
run_python.sh scripts are updated to build
and run the Python tests by building a
package and installing it in the developer's
Python 2.7 virtual environment.