Keep only command-line related functions in swiftlint module

[SimplyDanny]

Swift 6 doesn't allow importing executable targets. So we need to move testable logic into a framework.

[SwiftLintBot]

	1 Warning
⚠️	If this is a user-facing change, please include a CHANGELOG entry to credit yourself! You can find it at CHANGELOG.md.

	17 Messages
📖	Linting Aerial with this PR took 0.92s vs 0.95s on main (3% faster)
📖	Linting Alamofire with this PR took 1.28s vs 1.28s on main (0% slower)
📖	Linting Brave with this PR took 7.49s vs 7.46s on main (0% slower)
📖	Linting DuckDuckGo with this PR took 5.08s vs 5.09s on main (0% faster)
📖	Linting Firefox with this PR took 11.12s vs 11.03s on main (0% slower)
📖	Linting Kickstarter with this PR took 10.1s vs 10.09s on main (0% slower)
📖	Linting Moya with this PR took 0.53s vs 0.53s on main (0% slower)
📖	Linting NetNewsWire with this PR took 2.56s vs 2.55s on main (0% slower)
📖	Linting Nimble with this PR took 0.77s vs 0.77s on main (0% slower)
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📖	Linting Quick with this PR took 0.44s vs 0.43s on main (2% slower)
📖	Linting Realm with this PR took 4.73s vs 4.7s on main (0% slower)
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📖	Linting Swift with this PR took 4.63s vs 4.59s on main (0% slower)
📖	Linting VLC with this PR took 1.26s vs 1.26s on main (0% slower)
📖	Linting Wire with this PR took 18.35s vs 18.21s on main (0% slower)
📖	Linting WordPress with this PR took 11.88s vs 11.79s on main (0% slower)

Here's an example of your CHANGELOG entry:

* Keep only command-line related functions in `swiftlint` module.  
  [SimplyDanny](https://github.com/SimplyDanny)
  [#issue_number](https://github.com/realm/SwiftLint/issues/issue_number)

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[mildm8nnered]

lgtm, and compiles and tests fine on my outdated Xcode 15.2