Add Duplicate Imports Rule

[jpsim]

This is #2004, but from a branch on this repo to work around danger/danger#1034

[SwiftLintBot]

	13 Warnings
⚠️	This PR introduced a violation in Firefox: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Firefox/Sync/EncryptedJSON.swift:9:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Kickstarter: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Kickstarter/Library/TestHelpers/XCTestCase+AppEnvironment.swift:8:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Kickstarter: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Kickstarter/Library/ViewModels/MessagesSearchViewModel.swift:4:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Kickstarter: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Kickstarter/Library/ViewModels/SearchViewModel.swift:4:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/Migration.swift:21:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/List.swift:21:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/Object.swift:21:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/RealmConfiguration.swift:21:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/Realm.swift:21:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/Sync.swift:20:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/Tests/MigrationTests.swift:22:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in Realm: /Users/vsts/agent/2.144.0/work/1/s/osscheck/Realm/RealmSwift/Tests/TestCase.swift:21:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)
⚠️	This PR introduced a violation in WordPress: /Users/vsts/agent/2.144.0/work/1/s/osscheck/WordPress/WordPress/Classes/ViewRelated/Aztec/ViewControllers/AztecPostViewController.swift:13:1: warning: Duplicate Imports Violation: Imports should be unique. (duplicate_imports)

	12 Messages
📖	Linting Aerial with this PR took 1.8s vs 1.72s on master (4% slower)
📖	Linting Alamofire with this PR took 3.53s vs 3.46s on master (2% slower)
📖	Linting Firefox with this PR took 12.1s vs 12.04s on master (0% slower)
📖	Linting Kickstarter with this PR took 19.12s vs 19.39s on master (1% faster)
📖	Linting Moya with this PR took 1.88s vs 1.9s on master (1% faster)
📖	Linting Nimble with this PR took 1.88s vs 1.95s on master (3% faster)
📖	Linting Quick with this PR took 0.55s vs 0.58s on master (5% faster)
📖	Linting Realm with this PR took 3.35s vs 3.35s on master (0% slower)
📖	Linting SourceKitten with this PR took 1.14s vs 1.16s on master (1% faster)
📖	Linting Sourcery with this PR took 4.44s vs 4.51s on master (1% faster)
📖	Linting Swift with this PR took 25.68s vs 27.29s on master (5% faster)
📖	Linting WordPress with this PR took 19.42s vs 19.51s on master (0% faster)

Generated by 🚫 Danger

[jpsim]

Continuing in #2004.