SwiftFixIt: make some of the private API more public

This extends the visibility of some of the private implementation to the
package level to allow use for testing without `@testable` imports.

Author: compnerd

Sources/SwiftFixIt/SwiftFixIt.swift

@@ -43,15 +43,15 @@ private enum Error: Swift.Error {
 }
 
 // FIXME: An abstraction for tests to work around missing memberwise initializers in `TSCUtility.SerializedDiagnostics`.
-protocol AnySourceLocation {
+package protocol AnySourceLocation {
     var filename: String { get }
     var line: UInt64 { get }
     var column: UInt64 { get }
     var offset: UInt64 { get }
 }
 
 // FIXME: An abstraction for tests to work around missing memberwise initializers in `TSCUtility.SerializedDiagnostics`.
-protocol AnyFixIt {
+package protocol AnyFixIt {
     associatedtype SourceLocation: AnySourceLocation
 
     var start: SourceLocation { get }
@@ -60,7 +60,7 @@ protocol AnyFixIt {
 }
 
 // FIXME: An abstraction for tests to work around missing memberwise initializers in `TSCUtility.SerializedDiagnostics`.
-protocol AnyDiagnostic {
+package protocol AnyDiagnostic {
     associatedtype SourceLocation: AnySourceLocation
     associatedtype FixIt: AnyFixIt where FixIt.SourceLocation == SourceLocation
 
@@ -216,7 +216,7 @@ package struct SwiftFixIt /*: ~Copyable */ { // TODO: Crashes with ~Copyable
         )
     }
 
-    init<Diagnostic: AnyDiagnostic>(
+    package init<Diagnostic: AnyDiagnostic>(
         diagnostics: some Collection<Diagnostic>,
         categories: Set<String>,
         fileSystem: any FileSystem