Protobuf uses Guava 30.1.1, so I upgrade it at the same time. It also
caused an update to rules_jvm_external and reworking the Bazel build.
Protobuf no longer requires bind() so they were dropped. Although
Protobuf's protobuf_deps() brings in rules_jvm_external, and so we don't
need to define it ourselves, it seems better to define it directly and
not depend on transitive deps since we use it directly.
Protobuf now has support for maven_install() by exposing
PROTOBUF_MAVEN_ARTIFACTS, which required reorganizing the WORKSPACE to
use maven_install() after loading protobuf. Protobuf still doesn't
define target overrides for itself so we still maintain those. When
reorganizing the WORKSPACE I noticed http_archive should ideally be
above io_grpc_grpc_java as most users will need it there, so I fixed
that since there were lots of other load()-reordering already.
This version works around a warning about DuplicateStrategy in Gradle 6
that will be an error in Gradle 7 caused by [a bug in the plugin][1].
Bumping the version makes a clean build with `--warning-mode all` (at
least if skipping Android and codegen).
[1]: https://github.com/google/protobuf-gradle-plugin/issues/470
--secure was moved to front since many languages need flags to precede
positional parameters, and we'd like other languages to use the same
flags when feasible.
:8000 was removed from xds: target in the README, as it isn't all that
useful and is confusing as xDS itself provides the backend port numbers.