Add identical_operands opt-in rule

[marcelofabri]

Fixes #1371.

This rule was made opt-in because it's kind of slow to run 🐢

[SwiftLintBot]

	11 Warnings
⚠️	Big PR
⚠️	This PR introduced a violation in Firefox: /Users/distiller/project/osscheck/Firefox/Client/Frontend/Browser/BrowserViewController.swift:2327:46: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Kickstarter: /Users/distiller/project/osscheck/Kickstarter/KsApi/ServiceTests.swift:18:19: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Kickstarter: /Users/distiller/project/osscheck/Kickstarter/KsApi/ServiceTests.swift:19:19: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Kickstarter: /Users/distiller/project/osscheck/Kickstarter/KsApi/ServiceTests.swift:20:19: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Kickstarter: /Users/distiller/project/osscheck/Kickstarter/KsApi/ServiceTests.swift:21:19: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Swift: /Users/distiller/project/osscheck/Swift/stdlib/private/StdlibUnittest/StdlibUnittest.swift:2659:7: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Swift: /Users/distiller/project/osscheck/Swift/stdlib/private/StdlibUnittest/StdlibUnittest.swift:2665:7: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Swift: /Users/distiller/project/osscheck/Swift/stdlib/private/StdlibUnittest/StdlibUnittest.swift:2670:16: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Swift: /Users/distiller/project/osscheck/Swift/stdlib/private/StdlibUnittest/StdlibUnittest.swift:2675:16: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)
⚠️	This PR introduced a violation in Swift: /Users/distiller/project/osscheck/Swift/stdlib/public/core/KeyPath.swift:461:10: warning: Identical Operands Violation: Comparing two identical operands is likely a mistake. (identical_operands)

	12 Messages
📖	Linting Aerial with this PR took 0.44s vs 0.38s on master (15% slower)
📖	Linting Alamofire with this PR took 3.78s vs 3.22s on master (17% slower)
📖	Linting Firefox with this PR took 14.82s vs 12.37s on master (19% slower)
📖	Linting Kickstarter with this PR took 20.11s vs 18.45s on master (8% slower)
📖	Linting Moya with this PR took 2.02s vs 2.28s on master (11% faster)
📖	Linting Nimble with this PR took 1.8s vs 2.15s on master (16% faster)
📖	Linting Quick with this PR took 0.54s vs 0.58s on master (6% faster)
📖	Linting Realm with this PR took 3.37s vs 3.39s on master (0% faster)
📖	Linting SourceKitten with this PR took 1.09s vs 1.11s on master (1% faster)
📖	Linting Sourcery with this PR took 4.69s vs 4.9s on master (4% faster)
📖	Linting Swift with this PR took 28.48s vs 29.87s on master (4% faster)
📖	Linting WordPress with this PR took 18.75s vs 18.07s on master (3% slower)

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