Auto-quote introspected PostgreSQL identifiers

[morozov]

Schema managers for the platforms that respect SQL-92 with regard to identifier case sensitivity should introspect the identifiers with characters in lower case (or, for PostgreSQL, in upper case) as quoted. Otherwise, their actual case may get lost in translation.

Note

All identifiers should be always introspected as quoted but prior to #6589 (DBAL 5.0) it would be a BC break.

Currently, the Oracle schema manager does it via getQuotedIdentifierName(). The PostgreSQL one uses quote_ident() in schema introspection queries, but inconsistently, which leads to the bugs:

1. If an index column has upper-case letters, the column name isn't quoted. The first bug is covered by the reworked test.
2. If there are upper- and lower-case tables in the same schema (e.g. Users and users), all columns, indexes and foreign keys will be attributed to the lower-case one. This is covered by testDropWithAutoincrement(). If an upper-case table is introspected as unquoted, it will try to drop it without quoting the name and fail (because the database will automatically lower-case the unquoted name).

[morozov]

This isn't a problem per se. Whether the given schema manager will quote certain identifiers or not, we want to make sure that they are introspected in the proper case. Unfortunately, there's no public API to get the original case of an index or constraint column. For example:

1. Index::getColumns() returns lower-cased column names.
2. Index::getQuotedColumns() quotes the column names only if they are explicitly marked as quoted (e.g. by the Oracle or now PostgreSQL schema manager during introspection).

In DBAL 4.3, this issue no longer exists for foreign key constraints (#6728) but still exists for indexes. We will be able to run this test consistently on all platforms on DBAL 5.0.