Output is not deterministic for messages containing multiple `oneof` fields

[bkeryan]

The order of oneof fields in sabledocs-generated HTML varies from run to run.

Example:

syntax = "proto3";

package sable.test.v1;

message SampleMessage {
  string foo = 1;
  int32 bar =  2; 
  oneof test_oneof {
    string name = 4;
    int32 number = 9;
  }
  oneof test_oneof2 {
    string name2 = 5;
    int32 number2 = 10;
  }
  oneof test_oneof3 {
    string name3 = 6;
    int32 number4 = 11;
  }
}

Outputs from multiple runs with the same input:

Steps to reproduce:

protoc oneof-test.proto -o descriptor.pb --include_source_info
sabledocs

Context: my organization has an automated build that saves a build artifact if the build output is different from the most recent build artifact, and I noticed that it was saving near-identical build artifacts that differ only in the order of oneof fields in sabledocs-generated HTML. Based on https://github.com/markvincze/sabledocs/issues/31 I understand that the order is intended to be deterministic.

I suspect this may be related to using set to hold oneof_names: https://github.com/markvincze/sabledocs/blob/main/src/sabledocs/proto_descriptor_parser.py#L209

If that's the case, a potential solution may be to replace the set with a dict and use its keys view, which acts like a set but preserves order: https://docs.python.org/3/library/stdtypes.html#dict-views