Add new `ArrayConcatLiteral` cop to replace `a.concat([1, 2, 3])` with `a.push(1, 2, 3)`

Fixes #434

This PR is stacked on top of commits in #433.

ArrayConcatLiteral synergizes with ArrayPushSingle, so array.concat([x]) will be simplified down to just array << x

Before submitting the PR make sure the following are checked:

[x] The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
[x] Wrote good commit messages.
[x] Commit message starts with [Fix #issue-number] (if the related issue exists).
[x] Feature branch is up-to-date with master (if not - rebase it).
[x] Squashed related commits together.
[x] Added tests.
[x] 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.

rubocop / rubocop-performance