InnoDB is displaying table names in some diagnostic messages. Sometimes they
are translated, sometimes they are displayed directly in the internal
representation, which currently is "databasename/tablename" in the
filename-safe encoding. This is inconsistent.

table_name_t: Wrapper struct for pretty-printing table names.

operator<<(std::ostream&, const table_name_t&): Display table names.

innobase_convert_identifier(), add_identifier(): Use '`' instead of '"'
as the default quote character.

Clean up some tests, to allow them to be run with embedded server.

rb#6846 approved by Kevin Lewis and Mattias Jonsson