Add block_based_kvo rule

[marcelofabri]

Fixes #1714.

In theory, this could have false positives, but I think the chances are really low in practice. Depends on #1716.

[SwiftLintBot]

	12 Messages
📖	Linting Aerial with this PR took 0.36s vs 0.36s on master (0% slower)
📖	Linting Alamofire with this PR took 2.34s vs 2.52s on master (7% faster)
📖	Linting Firefox with this PR took 10.1s vs 10.47s on master (3% faster)
📖	Linting Kickstarter with this PR took 15.67s vs 14.85s on master (5% slower)
📖	Linting Moya with this PR took 0.71s vs 0.71s on master (0% slower)
📖	Linting Nimble with this PR took 1.44s vs 1.4s on master (2% slower)
📖	Linting Quick with this PR took 0.49s vs 0.46s on master (6% slower)
📖	Linting Realm with this PR took 2.27s vs 2.16s on master (5% slower)
📖	Linting SourceKitten with this PR took 0.83s vs 0.8s on master (3% slower)
📖	Linting Sourcery with this PR took 3.63s vs 3.62s on master (0% slower)
📖	Linting Swift with this PR took 10.73s vs 10.4s on master (3% slower)
📖	Linting WordPress with this PR took 10.72s vs 9.78s on master (9% slower)

Generated by 🚫 Danger

[codecov-io]

Codecov Report

Merging #1717 into master will increase coverage by <.01%.
The diff coverage is 87.5%.

@@            Coverage Diff             @@
##           master    #1717      +/-   ##
==========================================
+ Coverage   87.43%   87.43%   +<.01%     
==========================================
  Files         208      209       +1     
  Lines       10291    10323      +32     
==========================================
+ Hits         8998     9026      +28     
- Misses       1293     1297       +4

Impacted Files	Coverage Δ
Tests/SwiftLintFrameworkTests/RulesTests.swift	100% <100%> (ø)	⬆️
...e/SwiftLintFramework/Rules/BlockBasedKVORule.swift	85.71% <85.71%> (ø)

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