Implement dependency wrapping & version spec

Sources/apk/Index/ApkIndexDependency.swift

@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: Apache-2.0
+
+import Foundation
+
+struct ApkIndexDependency: ApkIndexRequirementRef {
+  let name: String
+  let versionSpec: ApkVersionSpecification
+
+  init(extract: String) throws(ApkRequirement.ParseError) {
+    (self.name, self.versionSpec) = try ApkRequirement.extract(blob: extract)
+  }
+}
+
+extension ApkIndexDependency: CustomStringConvertible {
+  var description: String {
+    switch self.versionSpec {
+    case .any: self.name
+    case .conflict: "!\(self.name)"
+    case .constraint(let op, let version): "\(self.name)\(op)\(version)"
+    }
+  }
+}