Bump protobuf from 2.27.1 to 3.1.0

[dependabot]

Bumps protobuf from 2.27.1 to 3.1.0.

Changelog

Sourced from protobuf's changelog.

Changelog

Changelog after version 3.0.0 lives in https://github.com/stepancheg/rust-protobuf/blob/master/CHANGELOG.md.

[3.0.0] - 2022-05-01

• New stable version released.

[3.0.0-alpha.14] - 2022-05-01

• JSON support is moved into a separate crate protobuf-json-mapping
• Generated code for well known types is more similar to regular protobuf now (well known type modules are now placed as is in well_known_types module instead of being flattened).
• file_descriptor_proto() function is private now in generated code. Descriptor can be obtained by calling file_descriptor().proto().
• file_descriptor() now returns &'static FileDescriptor
• Hide UnknownValues from public API (keep UnknownFields)

[3.0.0-alpha.13] - 2022-05-01

• More efficient reflective operations
• Fewer internals exposed from public API (e.g. ProtobufType is no longer public)

[3.0.0-alpha.12] - 2022-04-30

• keywords are now escaped with _ suffix
• generate trivial is_initialized functions when possible

[3.0.0-alpha.11] - 2022-04-29

• all fields are public now in generated messages
• protobuf-support crate added. This crate contains utilities shared by other protobuf crates. This crate has no public API.

[3.0.0-alpha.10] - 2022-04-11

• remove expose_oneof codegen option (it is on by default for a long time)
• remove unused serde-related options from rustproto.proto
• in generated code, enum variant names are converted to camel case
• generate SpecialFields field in messages instead of a pair (unknown_fields, cached_size)
• reflection operations like nested_messages now return iterator instead of Vec
• replace fn Enum::values() with const Enum::VALUES
• remove EnumFull::enum_descriptor(), does not provide much value over enum_descriptor_static
• rename EnumFull::enum_descriptor_static -> enum_descriptor
• fix EnumFull::descriptor for enums with allow_alias
• rename MessageDescriptor::enums to nested_enums
• rename MessageDescriptor::descriptor_static to descriptor
• add EnumDescriptor::enclosing_message()
• Message now requires PartialEq

... (truncated)

Commits

• c65c7d5 Bump version to 3.1.0
• 70cd66e Move clear_field reflection test
• 7f70813 Reflection clear_field tests
• d4aa230 Allow clearing field via reflection
• a9ca7ed Bump version to 3.1.0-pre
• 09c9c62 Bump version to 3.0.3
• 276a3cf set supported features (#626)
• 3585c2c Bump version to 3.0.2
• 6ff997e Fix generated mod.rs to pass cargo fmt -- --check
• 2bf4397 Erase changelog
• Additional commits viewable in compare view

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[remoun]

We currently use protoc-grpcio (in util/build/grpc/Cargo.toml) to generate the Rust code, but there's no new version to match. I filed mtp401/protoc-grpcio#41 to track this.

I tried switching to protobuf-codegen (published from the same repo as protobuf), and discovered that their v3 changes the generated code significantly: stepancheg/rust-protobuf#521
That's not necessarily a dealbreaker, but it would result in a big change touching a lot of files, which will require more care, and would make cherry-picking to and from release branches that much harder.

[jcape]

My own recommendation is that, if there's a bunch of churn to make this go we should just switch to prost.

[remoun]

Closing in favor of #2198

@dependabot ignore this major version

[dependabot]

OK, I won't notify you about version 3.x.x again, unless you re-open this PR or update to a 3.x.x release yourself.