[Ruby] Change constants lookup methods in enum class

Created by: miyucy

Module.constants and Module.const_get combination is slow.

See below benchmark:

class Sample
  CONST_0 = "0"
  CONST_1 = "1"
  CONST_2 = "2"
  CONST_3 = "3"
  CONST_4 = "4"
  CONST_5 = "5"
  CONST_6 = "6"
  CONST_7 = "7"
  CONST_8 = "8"
  CONST_9 = "9"

  def self.all_vars
    @all_vars ||= %w[0 1 2 3 4 5 6 7 8 9].freeze
  end

  def build_from_hash(value)
    constantValues = Sample.constants.select { |c| Sample::const_get(c) == value }
    raise "Invalid ENUM value #{value} for class Sample" if constantValues.empty?
    value
  end

  def new_build_from_hash(value)
    return value if Sample.all_vars.include?(value)
    raise "Invalid ENUM value #{value} for class Sample"
  end
end

require "benchmark/ips"

sample = Sample.new
values = %w[0 1 2 3 4 5 6 7 8 9].cycle
Benchmark.ips do |x|
  x.report("old build_from_hash") { sample.build_from_hash(values.next) }
  x.report("new build_from_hash") { sample.new_build_from_hash(values.next) }
end

Output:

Warming up --------------------------------------
 old build_from_hash    36.992k i/100ms
 new build_from_hash   239.730k i/100ms
Calculating -------------------------------------
 old build_from_hash    367.852k (± 6.2%) i/s -      1.850M in   5.050468s
 new build_from_hash      2.303M (± 7.7%) i/s -     11.507M in   5.029757s

So, I want to introduce new constants lookup method.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh

  Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (6.1.0) (minor release - breaking changes with fallbacks), 7.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

cc/ @cliffano (2017/07) @zlx (2017/09) @autopp (2019/02)