Re-export SwiftLintCore import in SwiftLintFramework

Because the core functionality is always useful when building rules, I'm
opting to import SwiftLintCore in SwiftLintFramework as `@_exported` so
that it's implicitly available to all files in SwiftLintFramework
without needing to import it directly.

.swiftlint.yml

@@ -62,8 +62,9 @@ number_separator:
   minimum_length: 5
 file_name:
   excluded:
-    - SwiftSyntax+SwiftLint.swift
+    - Exports.swift
     - GeneratedTests.swift
+    - SwiftSyntax+SwiftLint.swift
     - TestHelpers.swift
 
 balanced_xctest_lifecycle: &unit_test_configuration
@@ -101,3 +102,4 @@ custom_rules:
 unused_import:
   always_keep_imports:
     - SwiftSyntaxBuilder # we can't detect uses of string interpolation of swift syntax nodes
+    - SwiftLintFramework # now that this is a wrapper around other modules, don't treat as unused

Source/SwiftLintFramework/Exports.swift

@@ -0,0 +1 @@
+@_exported import SwiftLintCore