The ``has_table`` method now also checks views

The ``has_table`` method now also checks views

The :meth:`_engine.Inspector.has_table` method will now consistently check
for views of the given name as well as tables. Previously this behavior was
dialect dependent, with PostgreSQL, MySQL/MariaDB and SQLite supporting it,
and Oracle and SQL Server not supporting it. Third party dialects should
also seek to ensure their :meth:`_engine.Inspector.has_table` method
searches for views as well as tables for the given name.

Fixes: #7161
Change-Id: I9e523c76741b19596c81ef577dc6f0823e44183b