Removed DatabaseIntrospection.table_name_converter()/column_name_converter()
and use instead DatabaseIntrospection.identifier_converter().
Removed DatabaseFeatures.uppercases_column_names.
Thanks Tim Graham for the initial patch and review and Simon Charette
for the review.
Added a test for constraint names in the database.
Updated SQLite introspection to use sqlparse to allow reading the
constraint name for table check and unique constraints.
Co-authored-by: Ian Foote <python@ian.feete.org>