CAST Oracle table_name, owner, others to VARCHAR(128)

CAST Oracle table_name, owner, others to VARCHAR(128)

Added a CAST(VARCHAR2(128)) to the "table name", "owner", and other
DDL-name parameters as used in reflection queries against Oracle system
views such as ALL_TABLES, ALL_TAB_CONSTRAINTS, etc to better enable
indexing to take place against these columns, as they previously would be
implicitly handled as NVARCHAR2 due to Python's use of Unicode for strings;
these columns are documented in all Oracle versions as being VARCHAR2 with
lengths varying from 30 to 128 characters depending on server version.
Additionally, test support has been enabled for Unicode-named DDL
structures against Oracle databases.

Fixes: #4486
Change-Id: I2787e3f8de1f656318692bd535d6a7f1cef1a841