[DBAL-831] Fix explicit case sensitive identifiers in Oracle

This is a patch for https://github.com/doctrine/dbal/pull/540.

It includes the following bugfixes:

- Makes normalization of internally stored assets names consistent in `Doctrine\DBAL\Schema\Table`
- Fixes SQL generation for autoincrement columns with explicitly quoted table/column names in Oracle.
- Oracle identifiers that have been stored with explicit quotation are now correctly reverse-engineered by explicitly quoting them again in the schema manager (to preserve case). This only applies to identifiers that are not all uppercase (which indicated that they have been stored with a non-standard case).