Edited Feature: Allow DbContext to be created with an already-open existing connection plus ensure connection closing is consistent with opening [45]

DbContext can only be created with a closed connection, there are scenarios where it would be helpful if the connection could be open when creating the context (such as sharing a connection between components where we can not guarantee the state of the connection).<br /><br />The state of the EntityConnection and DbConnection should also be kept in sync.<br /><br />This item was migrated from the DevDiv work item tracking system [ID=7992]. <br />