[5.5] Fix column listing for postgres db driver.

[ghost]

PR for fixing issue #19496

Reminder

When postgresql database have multiple schemas, if you have the same table name in 2 different schemas then the getColumnListing() method will not return columns of the table that is in the currently used schema bu columns that are in the 2 tables.
This is due to compileColumnListing() method that does not consider the schema name of the table.

According to what was made in this PR #15535, I only consider the first schema if it's defined as an array in the configuration file.

Changes

• Add getColumnListing() method in Illuminate\Database\Schema\PostgresBuilder.
• Update compileColumnListing() method in Illuminate\Database\Schema\Grammars\PostgresGrammar to filter listing by schema name too.

[taylorotwell]

@themsaid can you verify this doesn't cause any issues with Postgres and works as expected?

[themsaid]

Yes I believe it'll work as expected, the breaking part is that in 5.4 a check if a table exists will pass if the table exist in any schema, in 5.5 with this PR it'll only pass if the table exists in the default schema.