Adds FoundationTypes and adds function to import individual types from modules (#504)

* Adds FoundationTypes and adds import

* Adds amazon file header and runs formatter

Author: Ed Paulosky

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/FoundationTypes.kt

@@ -0,0 +1,17 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0.
+ */
+
+package software.amazon.smithy.swift.codegen
+
+import software.amazon.smithy.swift.codegen.model.buildSymbol
+
+object FoundationTypes {
+    val TimeInterval = builtInSymbol("TimeInterval")
+}
+
+private fun builtInSymbol(symbol: String) = buildSymbol {
+    name = symbol
+    namespace = "Foundation"
+}

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/SwiftWriter.kt

@@ -110,6 +110,12 @@ class SwiftWriter(private val fullPackageName: String) : CodeWriter() {
         imports.addImport("Foundation", false)
     }
 
+    // Adds an import statement that imports the individual type from the specified module
+    // Example: addIndividualTypeImport("struct", "Foundation", "Date") -> "import struct Foundation.Date"
+    fun addIndividualTypeImport(kind: String, module: String, type: String) {
+        imports.addImport("$kind $module.$type", false)
+    }
+
     fun addImportReferences(symbol: Symbol, vararg options: SymbolReference.ContextOption) {
         symbol.references.forEach { reference ->
             for (option in options) {