Add new Performance/MapMethodChain cop

[koic]

This PR adds new Performance/MapMethodChain cop that checks if the map method is used in a chain.

# bad
array.map(&:foo).map(&:bar)

# good
array.map { |item| item.foo.bar }

Safety

This cop is unsafe because false positives occur if the number of times the first method is executed affects the return value of subsequent methods.

class X
  def initialize
    @@num = 0
  end

  def foo
    @@num += 1
    self
  end

  def bar
    @@num * 2
  end
end

[X.new, X.new].map(&:foo).map(&:bar) # => [4, 4]
[X.new, X.new].map { |x| x.foo.bar } # => [2, 4]

Benchmark

$ cat map_chain.rb
#!/usr/local/bin/ruby

require 'benchmark/ips'

Benchmark.ips do |x|
ary = %i[hi bye]

x.report('map.map') { ary.map(&:to_s).map(&:length) }
x.report('map')     { ary.map { |item| item.to_s.length } }

x.compare!
end

$ ruby -v
ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-darwin19]

$ ruby map_chain.rb
Warming up --------------------------------------
map.map   215.877k i/100ms
map   319.746k i/100ms
Calculating -------------------------------------
map.map      2.116M (± 2.1%) i/s -     10.578M in   5.002379s
map      3.227M (± 2.8%) i/s -     16.307M in   5.058091s

Comparison:
map:  3226860.1 i/s
map.map:  2115551.0 i/s - 1.53x  slower

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.