[Protobuf] Fix support for AllOf in protobuf-schema

[OpenGuidou]

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Description

This fix is in 2 steps:

Fixed index for vars in generated protobuf files

To ensure the backward compatibility between two schema generations, I'm fixing the index generated for each attribute base on its name.

Correct support of AllOf

As there is no inheritance in protobuf, the use case 3_0/allOf_composition_discriminator.yaml doesn't work.
If the parent is referenced in the response, we can't use one of its children as instantiation (Dog for Pet for example).
The only way to make it work is to replicate all attributes from the children in the parents, including imports.

Before the fix, the generated Pet was:

syntax = "proto3";

package somepackage;

message Pet {

  string petType = 0;

}

After the fix:

syntax = "proto3";

package somepackage;

import public "models/lizard_all_of.proto";
import public "models/snake_all_of.proto";
import public "models/cat_all_of.proto";
import public "models/dog_all_of.proto";

message Pet {

  string petType = 140636936;

  bool hasLegs = 159828448;

  bool lovesRocks = 499337491;

  string name = 3373707;

  string bark = 3016376;

}