Improve the performance of `WP_List_Table::get_column_info()` by adding the primary column to the cached header values. This reduces the number of calls to the `WP_List_Table::get_primary_column_name()` method to once per table in line with the other header getter functions.
Props bobbingwide, chaion07, costdev, mikeschroder, mukesh27, peterwilsoncc, shetheliving, spacedmonkey.
Fixes#34564.
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