Remove extensions from LowerACLThanBodyRule

Because of some oddities in the Swift extension ACL ruless, linting ACL
inside extensions isn't trivial because of a few cases:

1. Extensions cannot be open, but members inside them can:

```
open extension Foo { // Not valid
    open func bar() {}
}
```

2. Extensions cannot have an ACL modifier if they conform to a protocol:

```
public extension Foo: Bar {} // Not valid
```

3. Extensions that do have an ACL modifier affects the inner body,
making changes to this slightly riskier:

```
public extension Foo {
    func bar() {} // implicitly public
}
```

With this change we just sidestep all these problems, and instead opt to
only lint non extension types. I think this tradeoff is worth it so that
this can be enabled and catch issues in classes/structs/enums

Rules.md

@@ -8483,6 +8483,10 @@ fileprivate struct Foo { private func bar() {} }
 private struct Foo { private func bar(id: String) }
 ```
 
+```swift
+extension Foo { public func bar() {} }
+```
+
 ```swift
 private func foo(id: String) {}
 ```
@@ -8495,10 +8499,6 @@ private func foo(id: String) {}
 struct Foo { public func bar() {} }
 ```
 
-```swift
-extension Foo { public func bar() {} }
-```
-
 ```swift
 enum Foo { public func bar() {} }
 ```

Source/SwiftLintFramework/Models/AccessControlLevel.swift

@@ -51,10 +51,10 @@ extension AccessControlLevel: Comparable {
     private var priority: Int {
         switch self {
         case .private: return 1
-        case .fileprivate: return 2
-        case .internal: return 3
-        case .public: return 4
-        case .open: return 5
+        case .fileprivate: return 1
+        case .internal: return 2
+        case .public: return 3
+        case .open: return 4
         }
     }
 

Source/SwiftLintFramework/Rules/LowerACLThanBodyRule.swift

@@ -27,14 +27,14 @@ public struct LowerACLThanParentRule: OptInRule, ConfigurationProviderRule {
             "open class Foo { open func bar() {} }",
             "fileprivate struct Foo { private func bar() {} }",
             "private struct Foo { private func bar(id: String) }",
+            "extension Foo { public func bar() {} }",
+            "private struct Foo { fileprivate func bar() {} }",
             "private func foo(id: String) {}"
         ],
         triggeringExamples: [
             "struct Foo { public func bar() {} }",
-            "extension Foo { public func bar() {} }",
             "enum Foo { public func bar() {} }",
             "public class Foo { open func bar() }",
-            "private struct Foo { fileprivate func bar() {} }",
             "class Foo { public private(set) var bar: String? }"
         ]
     )
@@ -70,17 +70,16 @@ public struct LowerACLThanParentRule: OptInRule, ConfigurationProviderRule {
 private extension SwiftDeclarationKind {
     var isRelevantDeclaration: Bool {
         switch self {
-        case .`associatedtype`, .enumcase, .enumelement, .functionAccessorAddress,
-             .functionAccessorDidset, .functionAccessorGetter, .functionAccessorMutableaddress,
-             .functionAccessorSetter, .functionAccessorWillset, .functionDestructor, .genericTypeParam, .module,
-             .precedenceGroup, .varLocal, .varParameter:
+        case .`associatedtype`, .enumcase, .enumelement, .`extension`, .`extensionClass`, .`extensionEnum`,
+             .extensionProtocol, .extensionStruct, .functionAccessorAddress, .functionAccessorDidset,
+             .functionAccessorGetter, .functionAccessorMutableaddress, .functionAccessorSetter,
+             .functionAccessorWillset, .functionDestructor, .genericTypeParam, .module, .precedenceGroup, .varLocal,
+             .varParameter:
             return false
-        case .`class`, .`enum`, .`extension`, .`extensionClass`, .`extensionEnum`,
-             .extensionProtocol, .extensionStruct, .functionConstructor,
-             .functionFree, .functionMethodClass, .functionMethodInstance, .functionMethodStatic,
-             .functionOperator, .functionOperatorInfix, .functionOperatorPostfix, .functionOperatorPrefix,
-             .functionSubscript, .`protocol`, .`struct`, .`typealias`, .varClass,
-             .varGlobal, .varInstance, .varStatic:
+        case .`class`, .`enum`, .functionConstructor, .functionFree, .functionMethodClass, .functionMethodInstance,
+             .functionMethodStatic, .functionOperator, .functionOperatorInfix, .functionOperatorPostfix,
+             .functionOperatorPrefix, .functionSubscript, .`protocol`, .`struct`, .`typealias`, .varClass, .varGlobal,
+             .varInstance, .varStatic:
             return true
         }
     }