Annotate code specific to API Level 23 and above in AWSKeyValueStore (#786)

* Secure information stored in SharedPreferences

* Lower aws-android-sdk-core-test compile and target sdk version to 27

* Add a symlink to android-23.jar for core

* Add a gradle task that creates a symlink to android-23.jar for AWS Core

* Fix the gradle task that creates symbolic link to android-23.jar

* Change config.yml to setup android-23

* Enable core, cognitoidentityprovider and cognitoauth integration tests on CircleCI

* Enable core, cognitoidentityprovider and cognitoauth integration tests on CircleCI

* Fix pom.xml

* Improve exception handling in AWSKeyValueStore

* [2.12.3] Bump the patch version of 2.12.z

* Update 2.12.3 CHANGELOG

* Add the missing bucket prefixes to CleanupBucketIntegrationTests

* Fix a bug where migrating expirationDate in CognitoCachingCredentialsProvider crashes

* [2.12.4] Update changelog and bump version

* Annotate code specific to API Level 23 and above in AWSKeyValueStore

Author: Karthikeyan

aws-android-sdk-core/src/main/java/com/amazonaws/internal/keyvaluestore/AWSKeyValueStore.java

@@ -196,9 +196,11 @@ public synchronized String get(String key) {
                     // Read from store -> Base64 decode -> decrypt -> convert to string
                     final String encryptedData = sharedPreferences.getString(actualKey, null);
                     byte[] iv = getInitializationVector(actualKey);
-                    String decryptedDataInString = decrypt(apiLevel >= ANDROID_API_LEVEL_23
-                            ? new GCMParameterSpec(CIPHER_AES_GCM_NOPADDING_TAG_LENGTH_LENGTH_IN_BITS, iv)
-                            : new IvParameterSpec(iv), encryptedData);
+                    String decryptedDataInString = decrypt(
+                            //@apiLevel23Start
+                            apiLevel >= ANDROID_API_LEVEL_23 ? new GCMParameterSpec(CIPHER_AES_GCM_NOPADDING_TAG_LENGTH_LENGTH_IN_BITS, iv) :
+                            //@apiLevel23End
+                            new IvParameterSpec(iv), encryptedData);
                     cache.put(key, decryptedDataInString);
                     return decryptedDataInString;
                 } catch (Exception ex) {
@@ -233,9 +235,11 @@ public void put(String key, String value) {
                 try {
                     // Encrypt
                     byte[] iv = generateInitializationVector();
-                    String encryptedData = encrypt(apiLevel >= ANDROID_API_LEVEL_23
-                            ? new GCMParameterSpec(CIPHER_AES_GCM_NOPADDING_TAG_LENGTH_LENGTH_IN_BITS, iv)
-                            : new IvParameterSpec(iv), value);
+                    String encryptedData = encrypt(
+                            //@apiLevel23Start
+                            apiLevel >= ANDROID_API_LEVEL_23 ? new GCMParameterSpec(CIPHER_AES_GCM_NOPADDING_TAG_LENGTH_LENGTH_IN_BITS, iv) :
+                            //@apiLevel23End
+                            new IvParameterSpec(iv), value);
 
                     // Persist
                     sharedPreferences