[Swift 4.1] Add redundant_set_access_control rule

[marcelofabri]

Fixes #1869

The more important thing here is not the rule itself, but we have to make a decision on how we're going to mark rules that won't work on older Swift compiler versions, as Swift 4.1 includes some SourceKit fixes and improvements that will provide us more information to create rules.

We also probably should hold merging this until we have CI running Swift 4.1. I just wanted to open the PR to get feedback on the minSwiftVersion approach.

I also didn't implement auto correct on purpose: I think this rule shouldn't be triggered frequently and when there're violations, the user should check whether the correct behavior would be actually use the same ACL for the setter or it was a mistake in the first place.

[SwiftLintBot]

	2 Warnings
⚠️	Big PR
⚠️	This PR introduced a violation in Firefox: /Users/distiller/project/osscheck/Firefox/Client/Frontend/Login Management/LoginListViewController.swift:371:5: warning: Redundant Set Access Control Rule Violation: Property setter access level shouldn't be explicit if it's the same as the variable access level. (redundant_set_access_control)

	12 Messages
📖	Linting Aerial with this PR took 0.37s vs 0.36s on master (2% slower)
📖	Linting Alamofire with this PR took 3.03s vs 3.12s on master (2% faster)
📖	Linting Firefox with this PR took 11.01s vs 10.88s on master (1% slower)
📖	Linting Kickstarter with this PR took 16.03s vs 15.73s on master (1% slower)
📖	Linting Moya with this PR took 1.85s vs 1.81s on master (2% slower)
📖	Linting Nimble with this PR took 1.49s vs 1.43s on master (4% slower)
📖	Linting Quick with this PR took 0.5s vs 0.49s on master (2% slower)
📖	Linting Realm with this PR took 3.11s vs 2.97s on master (4% slower)
📖	Linting SourceKitten with this PR took 0.94s vs 0.93s on master (1% slower)
📖	Linting Sourcery with this PR took 4.29s vs 4.35s on master (1% faster)
📖	Linting Swift with this PR took 18.33s vs 18.69s on master (1% faster)
📖	Linting WordPress with this PR took 13.8s vs 13.64s on master (1% slower)

Generated by 🚫 Danger

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@59584f1). Click here to learn what that means.
The diff coverage is 81.81%.

@@            Coverage Diff            @@
##             master    #2036   +/-   ##
=========================================
  Coverage          ?   89.63%           
=========================================
  Files             ?      257           
  Lines             ?    14924           
  Branches          ?      973           
=========================================
  Hits              ?    13377           
  Misses            ?     1529           
  Partials          ?       18

Impacted Files	Coverage Δ
Tests/SwiftLintFrameworkTests/TestHelpers.swift	77.01% <100%> (ø)
...ource/SwiftLintFramework/Models/SwiftVersion.swift	100% <100%> (ø)
...ce/SwiftLintFramework/Models/RuleDescription.swift	94.44% <100%> (ø)
Tests/SwiftLintFrameworkTests/RulesTests.swift	100% <100%> (ø)
...intFramework/Extensions/Dictionary+SwiftLint.swift	86.53% <100%> (ø)
...tLintFramework/Models/RuleList+Documentation.swift	100% <100%> (ø)
...ramework/Rules/RedundantSetAccessControlRule.swift	61.9% <61.9%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 59584f1...1a9a4f7. Read the comment docs.

[marcelofabri]

This is ready for review! It looks a huge PR, but most of the changes are in Rules.md.