add supports for customizable imports from plugins

Author: yzhou

Sources/ImmutableSwift/generating/plugins/ISCodable.swift

@@ -5,6 +5,10 @@ class ISCodable: ImmutableSwiftGeneratorPlugin {
         return false
     }
 
+    func imports() -> [String] {
+        return ["Foundation"]
+    }
+
     func superClasses() -> [String] {
         return ["Codable"]
     }

Sources/ImmutableSwift/generating/plugins/ISCoding.swift

@@ -38,6 +38,10 @@ class ISCoding: ImmutableSwiftGeneratorPlugin {
         return true
     }
 
+    func imports() -> [String] {
+        return ["Foundation"]
+    }
+
     func superClasses() -> [String] {
         return ["NSObject", "NSCoding"]
     }

Sources/ImmutableSwift/generating/plugins/ISCopying.swift

@@ -5,6 +5,10 @@ class ISCopying: ImmutableSwiftGeneratorPlugin {
         return true
     }
 
+    func imports() -> [String] {
+        return ["Foundation"]
+    }
+            
     func superClasses() -> [String] {
         return ["NSCopying"]
     }

Sources/ImmutableSwift/generating/plugins/ISHashable.swift

@@ -5,6 +5,10 @@ class ISHashable: ImmutableSwiftGeneratorPlugin {
         return false
     }
 
+    func imports() -> [String] {
+        return ["Foundation"]
+    }
+
     func superClasses() -> [String] {
         return ["Hashable"]
     }

Sources/ImmutableSwift/generating/plugins/PluginUtils.swift

@@ -1,6 +1,7 @@
 protocol ImmutableSwiftGeneratorPlugin {
     static var Name: String { get }
     func shouldUseClass() -> Bool
+    func imports() -> [String]
     func superClasses() -> [String]
     func postVariableDefinition(_ datamodel: DataModel) -> String
     func postConstructor(_ datamodel: DataModel) -> String