EnhancedClient: Dectect Ignored Encryption Tags due to Flatten

### Issue
The DB-ESDK for DynamoDB in Java MUST detect all IGNORED Encryption Tags.

An Ignored Encryption Tag is one that the DB-ESDK does not respect when encrypting or decrypting a DynamoDB Record.

As of PR https://github.com/aws/aws-database-encryption-sdk-dynamodb-java/pull/248 , the DB-ESDK for DynamoDB in Java ONLY detects Ignored tags
on a table schema if they are one deep (on a nested class).

PR #248 added a Test that documents Ignored Encryption Tags that are NOT yet Detected.

These Tags are Ignored as they are placed on Fields
also tagged to be Flattened by DynamoDB.

As such, the Fields are not included in the elements of the Table Schema currently parsed by the DB-ESDK.

Start by reading PR #248 and the test it added documenting ignored encryption tags that are not detected. Trace how the DynamoDB table schema parser handles flattened fields and verify that ignored tags at those fields are detected. Done means all ignored encryption tags, including tags on flattened fields, are detected during schema parsing.

Written by the indexing model from the issue text.