Support l_bracket SpecialFieldName r_bracket in optionValues

[visma-alexander-maslov]

protobuf.js version: 7.3.2

According to protobuf language specification option value in form of
MessageLiteralWithBraces = l_brace MessageTexFormat r_brace can have MessageLiteralFieldName represented as
l_bracket SpecialFieldName r_bracket (see Protobuf Text Format in spec).

Now https://github.com/protobufjs/protobuf.js/blob/master/src/parse.js#L638 checks only for the FieldName which equals to identifier but not for SpecialFieldName.

Valid proto (from Scalapb docs)

syntax = "proto3";

package mypkg;

import "scalapb/scalapb.proto";
import "scalapb/validate.proto";

option (scalapb.options) = {
  scope: PACKAGE
  [scalapb.validate.file] {
      validate_at_construction: true
      insert_validator_instance: true
      skip: false
  }
};

/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/pbjs.js:254
            throw err;
            ^

Error: illegal name '[' (option-values.proto, line 10)
    at illegal (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/parse.js:96:16)
    at parseOptionValue (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/parse.js:639:27)
    at parseOption (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/parse.js:627:27)
    at parse (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/parse.js:852:17)
    at process (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/root.js:127:30)
    at fetch (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/root.js:179:13)
    at Root.load (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/root.js:207:13)
    at Root.loadSync (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/node_modules/protobufjs/src/root.js:248:17)
    at Object.main (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/pbjs.js:245:18)
    at Object.<anonymous> (/home/.nvm/versions/node/v20.11.0/lib/node_modules/protobufjs-cli/bin/pbjs:4:16)

Node.js v20.11.0