Call Item_field::fix_outer_field only on first execution

During the second execution of a prepared statement or procedure, calling Item_field::fix_outer_field can be problematic. For example
TODO: pull example out of test in MDEV-35673

Amongst the many things that fix_outer_field does, it populates Item_field::depended_from, which points to the SELECT_LEX where the Item_field is resolved. As SELECT_LEX structures are durable across executions, we can use this to avoid calling fix_outer_field during subsequent executions, also avoid a lot of issues related to permanent transformations that happen during optimization in the first execution.